PB83-134882
Giardiasis in Washington State
Washington State Dept. of Social and Health
Services, Olympia
'983
9810*
Prepared for
Health Effects Research Lab.
Research Triangle Park, NC
Nov 82
EJBD
ARCHIVE
EPA
600-
1-
82-
016
U.S. DtpVtlMflt Of CflMMKt
National-Tecluiicsl kifomutiM Scrvto
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PB83-13U8B2
:PA-600/1-82-016
November 1982
GIARDIAS1S IN WASHINGTON STATE
b.V
Floyd Frost, Lucy Harter, Byron Plan,
Karen Fukutaki.and Bob Holman
Office of Public Health Laboratories and Epidemiology
Office of Environmental Health Programs
Department of Social and Health Services
State of Washington
Olympia, Washington 98508
Grant No. R 805809
Project Officer
Walter Jakubowski
Toxicology and Microbiology Division
Health Effects Research Laboratory
Cincinnati, Ohio 45268
HEALTH EFFECTS RESEARCH LABORATORY
OFFICE OF RESEARCH A«0 DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
KKOOUCCD 11
NATIONAL TECHNICAL
INFORMATION SERVICE
US. OIP*RIK(N1 Of COKMERCE I |O
SPRIKGflUD. »». 22161 UO L.T/1
•nr\Q\ Headquarters and Chemical Libraries
01 idl EPA West Bldg Room 3340
in nuaH-i^n Mailcode 3404T
II UUheulOn 1301 Constitution Ave NW
Washington DC 20004
"1*^**laW**BW8^^
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TECHNICAL REPORT DATA
tl'Uase tcaJ InHniciivns on iliercursc before completing)
. RtPORT NO.
tPA-600/1-82-016
2.
3. RECIPIENT'S ACCESSIOWNO.
PB83 134882
4. TITLE AND SUBTITLE
Giardiasis in Washington State
5. REPORT DATE
November 1982
6. PERFORMING ORGANIZATION CODE
7. AUTHORtSI
F. Frost, L. Hartcr, B. Plan, K. Fukutaki and B. Holman
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Office of Environmental Health Programs
Department of Social & Health Services
State of Washington
Olympia, WA 98508
10. PROGRAM ELEMENT NO,
C10A
11. CONTRACT/GRANT NO.
R805809
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. EPA, HERL, TMD
26 West St. Clair Street
Cincinnati, OH 45268
13. TYPE OF REPORT AND PERIOD COVCRE D
Final; July 1978-April. 1981
14. SPONSORING AGENCY CODE
EPA/600/11
18. SUPPLEMENTARY NOTES
16. ABSTRACT
The objective was to determine the potcncial for transmission of giardiasis through
approved drinking water supplies in Washington State. The project consisted of five
studies: the first was conducted during trapping seasons (1976-1979) and resulted in
examining of 656 beaver stool samples, 172 tnuskrat and 83 other animal stools.
Positivity for beaver was 10.8%, for muskra1:, 51.2%. No Giardia was found in other
mammals. The second study contacted 865 Giardia-infected Washington state residents to
identify likely sources or possible risk factors for infection. Clusters of ceses were
linked to day care centers, backpacker groups or sites for drawing water on outings and
foreign travel. No excess cases were observed for users of surface drinking water
supplies. The third study was a case-control study to identify risk factors for
giardiasis. Factors which appeared to place a person at increased risk included
consumption of untreated water, foreign travel and attendance at a day care center. The
fourth study examined water filtering techniques for recovery of Giardia cysts from
drinking water supplies and yielded improvements in recovery. The fifth study was a
stool survey of children in Skagit and Thurston counties. Overall prevalence of
infection was 7.1%. No differences in the prevalence were found by source of domestic
water (surface filtered, surface unfiltered, well or spring).
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Intestinal infections, watcrborne disease,
giardiasis, epidemiology, drinking water,
stool surveys
b. IDENTIFIERS/OPEN ENDED TERMS
Giardia, protozoa,
concentration methods
c. COSATI Held/Group
13. DISTRIBUTION STATEMENT
Release to Publ.:
19. SECURITY CLASS fTllilRtport)
unclassified
21. NO. OF PAGES
91
20. SECURITY CLASS (Thispage)
unclacsi ficd
22. PRICE
EPA Form 2220-1 (9-73)
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
ii
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FOREWORD
The many benefits of our modern, developing, industrial society are
accompanied by certain hazards. Careful assessment of the relative risk cf
existing and new man-made environmental hazards is necessary for the es-
tablishment of sound regulatory policy. These regulations serve to enhance
the quality of our environment in order.to promote the public health and
welfare and the productive capacity of our Nation's population.
The complexities of environmental problems originate in the deep
interdependent relationships between the various physical and biological
segments of man's natural and social world. Solutions to these environ-
mental problems require an integrated program of research and development
using input from a number of disciplines. The Health Effects Research
Laboratory conducts a coordinated environmental health research program in
inhalation toxicology, genetic toxicology, neurotoxicology, developmental
and experimental biology, and clinical studies using human volunteer
subjects. These studies address problems in air pollution, water pollu-
tion, non-ionizing radiation, environmental carcinogenesis, and the toxi-
cology of pesticides and other chemical pollutants. The Laboratory
participates in and provides data for the development and revision of
criteria documents on pollutants for which national ambient air quality and
water quality standards exist or are proposed, provides the data for
registration of new pesticides or proposed suspension of those already in
use, conducts research on hazardous and toxic materials, and is primarily
responsible fo* providing the health basis for non-ionizing radiation
st-ndards. Direct support to the regulatory function of the Agency is
provided in the form of expert testimony and preparation of affidavits as
well as expert advice to the Administrator to ass .ire the adequacy of
environmental regulatory decisions involving the protection of the health
and welfare of all U.S. inhabitants.
This report presents the results of several studies designed to obtain
information on the epidemiology of giardiasis with specific attention given
to the potential role of drinking water. With a better understanding of the
epidemiology of this disease, informed decisions can be made on the need for
standards, treatment requirements or guidance to prevent transmission of
disease through our water supplies.
F. 6. Hueter, Ph.D. "*
Director
Health Effects Research Laboratory
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ABSTRACT
This research project was initiated to determine the potential for
transmission of giardiasis through approved drinking water supplies
in Washington State. The project consisted of five separate studies.
The first study, a parasitological stool survey of commercially
trapped aquatic mammals, was conducted during each trapping season from
1976 to 1979 and resulted in the examination of 656 beaver stcol samples,
172 muskrat stools and 83 other animal stool samples. Positivity for beaver
was 10.8% while positivity for muskrat was 51.2%. No Giardia was found in
other trapped ^animals (nutria, mink, raccoon, river otter, bobcat, coyote,
lynx or mountain beaver).
The second study, a follow-up of human giardiasis cases identi-
fied through medical diagnostic laboratories, contacted a total of 865
Giardia infected Washington State residents and asked a series of
questions designed to identify likely sources or possible risk factors
for infection. Two outbreaks were identified which implicated domes-
tic drinking water as the source. Other clusters of cases were linked to
day care centers, backpacker groups or sites for drawing water on outings
and foreign travel. No excess of cases was observed for customers of
surface drinking water supplies.
The third study was a case-control study to identify risk factors
for qiardiasis. This study included 349 laboratory identified cases and
349 controls selected from directory assistance listings. Factors which
appeared to place a person at increased risk of qiardiasis incluued con-
sumption of untreated water, foreign travel (for adults) and attendance at
a day care center (for children under age 10).
The fourth study examined water filtering techniques for recovery
of Giardia cysts from drinking water supplies. Initial application
of thetechnique recovered cysts from several supplies not implicated
in giardiasis outbreaks, however laboratory testing of the technique
demonstrated very poor cyst recovery using the recommended filter appli-
cation and analysis techniques. Changes in the application and analysis
techniques (lower water pressure, use of a continuous flow centrifuge,
different filter fiber washing techniques, 1 micron filter, etc.) yielded
order of magnitude improvements in cyst recovery. As few as 3000 cysts in
500 gallons of water would be adequate for cyst identification under
conditions of low to medium turbidity.
The fifth study was a stool survey of 1 to 3 year old children 1n
1v
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Skagit and Thurston counties. Children were randomly selected from
birth certificate listings and parents were paid to submit 2 stool samples
for analysis. Overall prevalence of infection was 7.1% for the children
surveyed. No differences in the prevalence were found by source of domes-
tic water '(surface filtered, surface unfiltered, well or spring).
This report was submitted by the Washington State Department of Social
and Health Services, Office of Environmental Health Programs, in fulfillment
of Grant No. R-805809 from the U.S. Environmental Protection Agency. This
report covers a period from July 1, 1978 to April 1, 1981 and work was
completed as of December 31, 1981.
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CONTENTS
Foreword . i i i
Abstract 1 v
Figures vi i i
Tables viii
Acknowledgements x
1. Introduction 1
2. Conclusions 3
3. Recommendations 5
4 Animal Surveys 6
Materi al s and methods 6
Results 7
Discussion 8
5 Cyst Recovery Methods 17
Materi al s and methods 17
Preparation of cysts 17
Determination of cyst density 18
Laboratory filtering apparatus 18
Analysi s procedure 19
Millipore filter procedure 19
Alqal centrifuge procedure 19
Resu1ts 19
Discussion 19
6 'Case Follow-up and Case-Control Study 25
Methods 25
Results 26
Case clusters 26
Case follow-up and case-control study.. 31
B1 ascs 44
Comparison of cases matched and
unmatched 44
An examination of cases without
apparent exposures 48
7 Discussion 53
8 Human Stool Survey 57
Methods 57
Results 58
Discussion 59
References 62
Appendix A 64
Appendix B 72
Appendix C 79
vil
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FIGURES
Number Paoe
1 Schematic of laboratory c/st concentration experiment 21
TARLFS
Number Pace
1 dumber of Animals Examined and Percent Giardia-Positive
by Species and Trapoinq Season 10
? Prevalence of Giardia in Beaver and Muskrat by Age and
Traooinq Season 11
3 ftiardia-Positive Specimens by Month Trapped, Traoping
Season and Animal Species 12
4 Giardia-Positive Animals by Watershed and Trapping Season... 14
5 Parasite Association of Beaver and Muskrat by Trapping
Season and Parasite 15
6 Number of Infections Missed by Technique (<) 16
7 Cyst Recovery by Technique and Filter Pore Size 22
8 Results of Field Application of Orion Filter 23
9 Relative Risk Estimates - 87 Cases Age 0 to 9 35
10 Relative Risk Estimates - 180 Cases Age 10 to 35 36
11 Relative Risk Estimates - 82 Cases Over Aqe 39 37
12 Multlvariate Equations 38
13 Relative Risk Estimates - 87 Cases *qe 0 to 9 39
14 Relative Risk Estimates - 180 Cases Age 10 to 39 40
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TABLES (continued)
Number Paoe
15 Relative Risk Estimates - 82 Cases Over Age 39 41
16 Foreign Travel Destination for Cases and Controls 43
17 Relative Risk Estimates Calculated With (87 Cases) and
Without (74 Cases) the 11 Day Care Children 43
18 Matched vs Unmatched Cases 46
19 Aae-Sex Distribution (Residual Cases) 49
20 Presence of an Infant in the Household 49
21 Observed and Exoected Infants in the Household 50
22 Swimrni nq bv Aqe and Sex 50
23 Exposure by Season of Symptoms Onset 52
24 County by Month of Onset (Residual Cases) 51
25 Source of Domestic Water Supply by Exposure Group 52
?6 Positivitv by Type of Water Source 60
27 Positivity by Type of Recreation 60
28 Number of Children *n Household and Untreated Water
Consumption 61
29 Occupation of Participants and Controls 61
ix
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ACKNOWLEDGEMENTS
The authors wish to express appreciation for the support and encour-
agement of Dr. Jack Allard, Or. Donald Peterson, and Mr. William Miller.
In addition we wish to thank Mr. Walter Jakubowski and the Health Effects
Research Laboratory, USEPA for both financial and technical support for the
project and the Local iiedlth Departments of Washinaton State for their
assistance in reporting and following d.:.es. The authors also wish to
acknowledge the assistance of Kathy Perkins-Jones, Scott Sheffield, Mike
Thornley and the Washington State Game Department.
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SECTION 1
INTRODUCTION
Although Giardia infections in man have been recognized for centu-
ries, waterborne transmission of this parasite has only recently been
recognized as a ma.ior mode of dissemination. Drinking water contaminated
with human waste was thought to be the likely source 01 a giardiasis
outbreak in Aspen, Colorado in 1966. Contamination of water by aquatic
mammal waste was thought to be the likely source of outbreaks in Camas,
Washington (1976) and Berlin, New Hampshire (1976). ."he l?.'.ter outbreaks
ware of particular interest to water treatment engineers and public
health officials since the treated water met both coliform and turbidity
levels believed to protect against waterborne disease outbreaks. Further-
more, the conditions which resulted in the Camas outbreak were likely to
occur convnonly throughout Washington State and perhaps throughout much of
the West.
Following the Camas outbreak of Aoril and May 1976, the Washington
State Department of Social and Health Services (DSHS) together with
the Environmental Protection Aaency (EPA) began a series of investi-
gaticns to determine whether similar outbreaks were occurring elsewhere
in Washington State and to estimate the potential for future outbreaks.
The Camas outbreak was thought to be related to Giardia infected beaver
residing in the watershed of the town's surface water supply. Problems
with the Camas water filter system resulted in cysts (possibly excreted
from beaver) passing through the filter. They were probably unaffected by
the level of chlorination used at the time of the outbreak. The majorUy
of Washington State residents are served by surface water supplies and many
of these supplies use chlorinatio:i as the only means of disinfection.
Since all of these watersheds are frequented by beaver, the presence of
Giardia infected beaver could lead to similar outbreaks.
Information was required on both the potential for human exposure
to Giardia as well as whether human illness resulted. To determine the
extent of aquatic mammal infection with Giardia, stool surveys of com-
mercially trapped animals were initiate-! in the fall of 1976 and continued
through spring 1980. To begin assessing the extent of human Illness
resulting from giardiasis.. a pilot human case follow-up was initiated in
1977 and extended to a statewide human follow-up in July 1°78. To identify
risk factors for human giardiasis, a case-control stud> was initiated in
March 1979 and continued through March 1980 when case follow-up was also
suspended. In July 1978 an .ijwKtiqacion was initiated to estimate how
frequsntly Giardia cysts could be recovered from drinking water supplies
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usinq a laroe volume water filtration technique developed by the Health
Effects Research Laboratory (HERL) of the E?A. Due to problems with the
technique, this aspect of the study was modified so that more effort was
placed on evaluating alternative methods for cyst recovery. In Sep-
tember 1980 a human stool survey of one to three year old children was
initiated to determine whether a difference in prevalence of infection
existed between areas served by surface water supplies (Skaqit county) and
areas served by well water supplies (Thurston county).
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SECTION 2
CONCLUSIONS
This project demonstrated a widespread potential for waterborne
transmission of giardiasis in Washir.gton State. During the four years of
animal surveys, Giardia prevalence in beaver ranqed from 6% to 19% and in
muskrat from 0% to 85%. Infected beaver were found throughout the state
in both protected and unprotected watersheds which provide drinking
water for Washington State residents.
Statewide human qiardiasis surveillance efforts and follow-up sub-
stantially increased the number of reported giardiasis cases, identified
two outbreaks associated with domestic drinking water supplies, two out-
breaks associated with consuming untreated drinking water, two day care
center outbreaks, one outbreak associated with foreign travel and numerous
smaller clusters of cases. From the case-control study, foreign travel,
consumption of untreated water and attendance at a day care center (for
children) were found to be significantly more common among giardiasis cases
than controls. Among giardiasis cases with foreign travel, only travel to
Third World countries was found to be associated with giardiasis.
The human case follow-up revealed that giardiasis follows a bimodal
age distribution affecting both young children and young adults. Evi-
dence of secondary transmission was observed, especially within house-
holds having young children. No excess of cases was observep among
customers of surface water supplies, even after eliminating individuals
with other likely sources of infection {homosexuals, tnose wno consumed un-
treated surface water, day-care center attendees, persons with a history of
recent foreign travel, and case clusters with a likely common exposure).
Results of the stool survey of one to three year old children gen-
erally supported the findings of the case-control study and the human
case follow-up. No difference in Giardia prevalence was observed for
children served by deep well water supplies and surface supplies. In both
cases one to three year old-; were found to have a 7.1% prevalence of
Giardia. An increased risk of infection was found for children with
exposure to untreated surface water and for children with more than two
siblings between the age of thrfc«. and ten. No increased risk was found for
children attending day care centers, contradicting results of the case-
control study.
Environmental sampling to recover Giardia from natural waters proved
to be disappointing. Of the 77 water filter samples examined, only 5 were
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positive for Giardia and 3 of these were taken In response to a reported
outbreak. An examination of recovery efficiency was begun early in the
project to test the filter both in the field and in the laboratory.
Initial recovery of one cyst out of 30,000 cysts was followed by changes in
both the application and analysis procedures. These changes (lower water
pressures, more agitation to remove cysts from the filter fibers, and the
use of an Foerst centrifuge) resulted in recovery of nearly 10% of the
experi-.ientally added cysts. Concentration techniques using sucrose or zinc
sulfate were examined but did not provide noticeable improvements when used
on filter samples.
The implications of these findings for waterborne transmission of
giardiasis in Washington state are: 1) Giardia infection among aquatic
mammals in Washington is widespread, including animals in the most remote
and protected watersheds. 2} Although recovery of cysts from water
implicated in an outbreak has usually been possible, recovery of cysts
from other surface water was only occasionally possible. Although animal
trapping results suggest that cysts should be commonly found in surface
waters, the concentration of cysts required for filter recovery is seldom
observed. 3) With the exception of several outbreaks, Washington's surface
water supplies did not provide an increased risk of giardiasis or Giardia
infection for their customers. The suspected excess level of disease in
communities served by surface water supplies was not observed. Consumption
of untreated surface water, person to person transmission (primarily among
children), and travel to Third World countries were the most important risk
factors associated with giardiasis.
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SECTION 3
RECOMMENDATIONS
Waterborne qiardiasis does not appear to be a significant public
health problem in Washington State, despite the widespread potential
for water supply contamination. The waterborne outbreaks detected were
associated with operational problems (Leavenworth) and with inadequate
design (Boistfort) of treatment plants. No outbreaks were detected in
cither Tacoma or Seattle, even though infected animals were trapped from
the watersheds of the surface water supplies and the only treatment provid-
ed.is chlorinatior..
In contrast, untreated surface water does present a significant
public health problem. Consumption of untreated water was recognized as a
risk factor for giardiasis in all age groups and was also associated
with Giardia infection among stool survey participants.
Orion-wound filters proved to be useful in recovering cysts from
water supplies implicated in a human giardiasis outbreak but did not yield
useful information on water supplies randomly selected. Laboratory
evaluation of filter analysis procedures suggests that improvements in
recovery and reductions in cost can be achieved by using an algal (Foerst)
centrifuge rather than the series of screens recommended by earlier studies.
Results of the stool survey suggest that water contamination may
interact with other risk factors by providing an initial infection. The
number of children in a household appeared to be a risk factor, however the
risk was only increased among families with a history of untreated water
consumption.
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SECTION 4
ANIMAL SURVEYS
The first of the five projects to be described is a series of animal
surveys begun in November 1976 and continued through the 1979-80 trapping
season.. The surveys focused primarily on aquatic mammals and were made
possible with the co-operation of the commercial trappers and the State
Game Department.
Cross-transmission of Giardia from infected beaver to humans was
postulated as the likely source of a giardiasis outbreak in Camas, Wash-
ington in 1976 (1). The Boulder and Jones Creek watersheds, supplying
water to Camas, are characterized by extremely limited human activity and
the presence of varied wildlife species, including beaver. During the
outbreak investigation, Giardia cysts were recovered from both raw and
treated water. A total of twelve animals of various species were trapped
in each watershed and examineJ for Giardia. Three Giardia-infected beaver
were detected from areas above the intakes.
MATERIALS AND METHODS
Commercial trappers were recruited with the assistance of the State
Game Department to provide stool samples from trapped animals. Those who
agreed to participate were supplied with sampling kits containing vials,
mailing containers, instructions on how each sample was to be obtained and
a survey form. Samples were collected from the large intestine or rectum
of the animal using a stick included with each kit. The sample was then
placed in the vial and mailed to the State Public Health Laboratory.
During the second and third years, the vials contained either 2.5% formalin
or distilled water and, during the fourth year, 5% buffered formalin to
preserve the samples. One sample per animal was taken.
Trappers were encouraged to submit samples from municipal watersheds.
Special arrangements were made for trapping in protected watersheds. Dur-
ing the first year only beaver samples were requested. During the second,
third and fourth years samples from beaver, muskrat, mink, raccoon and
river otter were requested. Stool samples from other mammals were also
accepted and examined.
The stool samples were sent by mail to the State Public Health Labor-
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atory for analysis. All samples received were processed by the formalin-
ether (FE) sedimentation technique (2). If a delay occurred between
receiot and processing of the samples, they were refrigerated at 4* to 7*
C. until processed. In addition to the FE technique, the zinc sulfate (3)
and sucrose (4) centrifugal flotation techniques were used to examine
samples received during the fourth year of the survey. This was done to
determine if the analysis techniques might improve the estimated prevalence
of infection. Zinc sulfate (1.22 specific gravity) with 3 minutes of
centrifugation at 1000 rpm (180g) and sucrose (1.15 specific qravity) with
5 minutes of cer,.rifuqation at 2000 rpm (750g) were utilized in the res-
pective flotation techniques. A 22 mm square coverslip was superimposed on
each 15 ml centrifuge tube in contact with the flotation fluid prior to
centrifuqation. Samples processed by all techniques were examined micro-
scopically following staininq with Luqol's iodino. Coverslips were scanned
at lOx and suspect objects were examined at 45x. All parasites and eqqs
observed in samples submitted durinq the third and fourth seasons were
noted.
Samples were processed in numerical order in this fashion until all
samples had been examined. Samples positive for Giardia cysts were eval-
uated semi-quantitatively usinq the followinq scale"; T1 for 1-50 cysts/
coverslip, 2+ for 50-200 cysts/ coverslip, 3+ for 200-500 cysts/coven,lip,
and 4+ for 500+ cysts/coverslip.
Statistical analysis of the data was performed usinq t-tests and
Chi-square tests.
RESULTS
A total of 911 animal stool samples were submitted over the four
trapoinq seasons. Of these, 656 were from beaver, 172 from muskrat, 7 from
nutria, 12 from rrpnk, 2°> from raccoon, 19 from river otter, 8 from bobcat,
2 from coyote, 1 from a lynx, and 6 from mountain beaver. Samples were
received from 31 of 39 counties in Washington.
Parasites were found in the stools of all species of animals from
which samples were submitted. However, only beaver and muskrat specimens
were positive for Giardia (Table 1). The overall prevalence of Giardia
noted 1n beaver specimens ranged from 6% to 19%, while that in muskrat
ranqed from 0% to 8555. Giardia prevalence in muskrat specimens was higher
than in beaver specimens submitted durinq the third and fourth trappinq
seasons and, also when the data from the four trapping seasons were pooled
(p <0.01). A higher percentaqe of juvenile beaver specimens were positive
for Giardia than were specimens from adult beaver. The difference was
significant for the second, third and fourth trappinq seasons and, aqain,
when the data from all four surveys were pooled (p <0.01) (Table 2). For
muskrat no significant difference in prevalence by age class was observed.
The distributions of positive specimens by month trapped, trappinq season
and animal species revealed no consistent trends from year to year (Table
3). Positive animals were detected in 24 o* 31 counties surveyed over the
four trappinq seasons. Positive animals were detected in watersheds
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regardless of the level of watershed protection (Table 4).
Ho siqnificant differences were detected in the prevalences of other
rarasitic infections amonq Giardia-positive versus Giardia-neqative beaver
(Table 5). Inconsistent differences in the orevalences_of other parasitic
infections were observed for Giardia-positive versus Giardia-neqative
tnuskrat samples submitted durinq the second and third trapping season.
Analyses of the fourth year's data revealed no statistically sig-
nificant differences in the diagnostic oowers of the formalin-ether sedi-
mentation, zinc sulfate centrifugal flotation and sucrose centrifugal
flotation methods with respect to detection of Giardia cysts (Table 6).
The only siqnificant observed difference occurre3TrT the diagnosis of
trematode eggs. The formalin-ether technique recovered trematode eggs,
while the flotation procedures did not. There was some indication that the
sucrose technique was superior to the formalin-ether technique in the
recovery of coccidia cysts.
DISCUSSION
Giardia appears to :"3 a common intestinal parasite of beaver and
muskrat in Washington. The surveys conducted cannot be considered to have
randomly samoled either the beaver or muskrat population. The manner in
which specimens were obtained did not give equal probability of inclusion
for all animals in the state. If cyst excretion is as variable in infected
beaver and muskrat as it is in man, the use of a single stool specimen per
animal can be expected to underestimate the actual prevalence of Giardia in
these mammals. Thus, the prevalences estimated should be considered as
minimum prevalences of infection. Nevertheless, the data obtained indicate
a widespread distribution of Giardia infected aquatic mammals across the
state and therefore the potential for water contamination by aquatic
mammals. This may occur even in "protected" watersheds.
The data collected suggest that aquatic mammals in Washington can
obtain Giardia infections in the absence of human involvement. It is
possible~lnaF~an influx of infected animals into an area is a component of
the apparent svlvatic cycling of the parasite with the immigrating infected
animals infected via human- or animal-source contamination. However,
cross-transmission of Giardia may occur between various animal species
in the same ecosystem (5). It is also possible that once infected by
whatever means, these mammals maintain their infections, shedding cysts
periodically in response to undetermined factors, but frequently enough
to infect offspring. Beaver infected as juveniles might then infect
animals in other areas when they migrate as two-year-olds to establish
their own territories and colonies. Thus, the higher prevalence of infec-
tion or increased frequency of cyst shedding noted in juvenile versus adult
beaver may be of importance in parasite transmission.
The observed difference in prevalence of infection in juvenile versus
adult beaver cannot be totally explained from the collected data. Possible
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explanations include loss of infection in adulthood, decreased suscepti-
bility to infection with increased aqe, development of latent infections,
longer periodicity in cyst shedding, or lower levels of cyst sheddinq
increasing the difficulty of cyst detection. To further investigate these
possibilities, it would be necessary to collect intestinal tracts from
animals sampled and examine them for trophozoites or to monitor infected
animals in captivity from the tiire they are juveniles. A possible differ-
ence in prevalence with age in muskrats may become apparent with larger
sample sizes. It should be noted that the individual trappers were respon-
sible for determining the aqe classes of the animals trapped and, there-
fore, some errors may have been incorporated into the results.
It is unclear why both juvenile and adult muskrat demonstrated a
higher percentage of Giardia-positive stools than the corresponding age
classes of beaver. Perhaps muskrat more often shed cysts. Alternatively,
a greater proportion of areas containing Giardia-shedding animals may have
been sampled for muskrats than for beaver.
The results of the technique comparisons made during the fourth year
of the study suggest that using the formalin-ether sedimentation technique
did not affect the estimated prevalence of Gjardia infection. In fact,
it may be the technique of choice for this type of work because it concen-
trates a wide range of parasites and, based on this limited study, is as
sensitive as zinc sulf?.te and sucrose for identifying Giardia.
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TABLE 1. NUMBER OF ANIMALS EXAMINED AND PERCENT
GIARDIA-POSITIVE BY SPECIES AND TRAPPING SEASON
Species
Beaver
Muskrat
Nutria
Mink
*
Raccoon
River Otter
Bobcat
Coyote
Lynx
Mountain Beaver
Parasites
G,C,Tr,E,N
G,C,Tr,E,N,Ch,Tc
C.Tr
Tr.NJc
C,N,Tc
Tr
To
To
To
_Number_ Submitted
1976/1977 1977/1978
173 (6%) 178 (7%)
1 17 (35%)
2
5
4
1 2
(% Giardia-positive)
1978/1979 1979/1980
179
114
5
7
24
10
7
2
1
(19%) 126 (12£)
(42%) 40 (85%)
6
1
6
G = Giardia
sp. Ch =
C = coccidia Tr =
Chilomastix sp.
trematode eggs
To =
Tc =
Toxocara sp.
Trichuris sp.
E = Entamoeba muris
N = nematode eggs
-------
TABLE 2. PREVALENCE OF GIARD1A IN BEAVER AND MUSKRAT
BY AGE
AND TRAPPING SEASON
Juvenile
Animal Trapping Season G+
Beaver
Muskrat
1976-77
1977-78
1978-79
1979-80
1976-77
1977-78
1978-79
1979-80
5
8
17
8
38
0
0
12
J.
(%) Total*
(12)
(17)
(38)
(31)
(24)
(0)
(0)
(71)
(75)
43
47
45
26
161
0
0
17
_£
G+
6
4
14
7
31
0
5
36
31_
Adult
(%) Totjl#
(5)
(3)
(11)
(7)
(7)
(0)
(36)
(38)
(86)
123
127
129
97
476
1
14
95
Jl
G+
0
0
3
0
0
1
0
0
Unknown
(%) Total*
(0)
(0)
(60)
(0)
(0)
(33)
(0)
(0)
7
4
5
3
0
3
2
0
15 (71) 21 72 (49) 146
-------
Sept.
TABLE 3. GIAROIA-POSITIVE SPECIMENS BY MONTH TRAPPED,
TRAPPING SEASON AND ANIMAL SPECIES
Beaver
Muskrat
Month Trapoinq Season ^Examined #Giardja+ (%) * Examined #Giardia+ (%)
1976-1977
1977-1978'
1978-1979^
1979-1
-------
TABLE 3. (CONTINUED)
Bea1 er
Muskrat
Month Traoninq Season ^Examined #Giardia+ (1) # Examined fGiardia-*- (56)
Apr. 1976-1977
1977-1973
1978-1979
1979-1930
Unknown 1976-19?7
1977-1978
1978-1979
1979-1980
5
3
27
12
1
2
1
0
3
2
0
0
v'20)
(0)
(11)
(17) 4
(0)
(0)
-
2 (50)
-
(1) General Ooen Season: Eastern Washinoton: Beaver and Mink, 11/13/76-
12/31/76; ^uskrafTl/13/76-3/31/77; Raccoon, 11/13/76-2/28/77.
Western Washinnton: Beaver, Mink, River Otter, 11/20/76-12/31/76;
Muskrat and Raccoon, 11/20/76-2/28/77.
(2) General Open Season: Eastern Washinoton: beaver and Mink, 11/12/77-
W-ll/77; Muskrat, 11/12/77-3/31/78; Raccoon, 11/12/77-1/31/78.
Western Washinaton: Beaver, Mink, River Otter, 11/19/77-12/31/77;
Muskrat and Raccoon, 11/19/77-2/28/78.
(3) General Open Season: Eastern Washlnqton: Beaver and Mink, 11/11/78-
12/31/78; Muskrat, 11/11/78-3/31/79; Kaccoon, 11/11/78-1/14/79.
Western Washington: Beaver and River Otter, 11/18/78-12/31/78;
Muskrat, 11/18/79-2/28/79; Mink and Raccoon, 11/18/78-1/31/79.
(4) General Open Season: Eastern -Washington: Beaver and Mink, 11/10/79-
12/31/79; Muskrat, 11/10/79-3/31/80; Bobcat, 12/1/79-12/31/79.
Western Washington: Baaver and River Otter, 11/17/79-12/31/79;
Muskrat, 11/17/79 -2/29/80; Bobcat, 11/17/79-1/20/80.
13
-------
TABLE 4. GIARDIA-POSITIVE ANIMALS BY WATERSHED
AND TRAPPING SEASON
Means of
Watershed
Protection
Fences, gates,
patrolled
Signs posted,
gates
Open
County
King
King
King
Skaglt
Clark
Clark
Grays H.
Grays H.
Lewis
Pierce
Columbia
Klttltas
Pend Or.
Snohomi sh
Snohomish
Yaklma
Watershed 76-77
Cedar River
N.F. Tolt River
Green River
Judy Reservoir
Jones Creek X
Boulose Creek X
Wishkah River X
Davis Creek
N.F. Newaukum River
So. Prairie Creek
Touch et River X
Yaklma River
Pend Or. River
Pilchuck River X
Sultan Munic.
Naches River
77-78 78-79 79-80
X X
X
X
X
•
X
X
X
X X
xxx
X X
X
X
X X
14
-------
TABLE 5. PARASITE ASSOCIATIONS OF BEAVER AND MUSKRAT
BY TRAPPING SEASON AND PARASITES
Giardl a -positive
Species
Beaver
Number examined
No other parasites
Coccidia
Trematodes
Coccidia, trematodes
Coccidia, E. muris
Nematode eggs
Muskrat
Number examined
No other parasites
E. muris
Trematode
Coccidia
Nematode eggs
E. muris, other parasites
I)t her "comb 1 n a 1 1 on s
1978-79
34
67.6%
11.8*
11.8*
8.8*
48
16.7*
25.0*
16.7*
2.1*
20.8*
18.7*
1979-80
15
46.7%
46.7*
6.7*
34
32.4*
2.9*
5.9*
11.7*
5.9*
29.4%
11.8*
Giardia-
1978-79
145
57.9*
19.3*
15.9*
6.9*
66
42.4*
12.1*
24.2*
1.5*
13.6*
6.1%
negative
1979-80
111
48. 6*
24.2*
8.1*
6.3*
0.9*
1.8%
6
16.7*
33.3%
16.7*
16.7*
16.7*
15
-------
TABLE 6. NUMBER OF INFECTIONS MISSED BY TECHNIQUE (%)
o\
Animal
Beaver
Muskrat
Technique
Formalin-ether
Zinc sulfate
Sucrose
FormaTin-ether
Zinc sulfate
Sucrose
Trematode Nematode Trichuris-
Giardia Coccidia E. muris eggs larvae tyoe egg
2 (13%) 25 (47%) 1 (100%) 0 (0%) 2 (100%)
3 (20%) 20 (38%) 0 (0%) 17 (100%) 0 (0%)
6 (40%) 15 (28%) 1 (100%) 17 (100%) 1 (50%)
2 (6%) 9 (75%) 4 (31%) 0 (0%) 2 (20%) 0 (0%)
8 (24%) 6 (50%) 3 (23%) 13 (100%) 5 (50%) 1 (100%)
4 (12%) 3 (25%) 9 (69%) 13 (100%) 6 (60%) 1 (100%)
* Each sample was examined by each technique
-------
SECTION 5
CYST RECOVERY METHODS
Recovery of Giardia cysts from a water supply implicated in a giar-
diasis outbreak first occurred in Rome, New York in 1975 (6) and later
during outbreak investigations in Camas, Washington in 1976 (7) and Berlin,
Mew Hampshire in 1976 (8). Giardia cysts were also recovered from two
Washington State water supplies (Everett and Hoquiam) not implicated in
outbreaks.
The recovery of cysts from water supplies not implicated in giardiasis
outbreaks, toqether with widespread distribution of Giardia positive
beaver and muskrat found in aguatic manmal surveys (9), suggested likely
Giardia contamination of drinking water supplies. To ascertain the
extent of the problem, a project was initiated to evaluate cyst recovery
methods and then apply cyst recovery techniques to water supplies through-
out Washington state. The project began by filtering water with known cyst
concentrations to estimate cyst recovery. Two filters (7 urn and 1 um) and
two analysis procedures were examined. The project then apolied the
technique to 18 surface water supplies in Washington state.
MATERIALS AND METHODS
Evaluation of cyst recovery required a cyst supply and en experimental
apparatus to simulate field conditions. Since only a few parameters could
be examined, due to the considerable time each filter run involved, it was
decided to compare recovery using the 7 urn versus the 1 urn filter on three
cyst concentrations and compare two analysis techniques (the Foerst centri-
fuge versus gravity fed filters) on split samples from each filter run.
Preparation of Cysts
Approximately 3 ml of formalized feces from at least two human donors
were comminuted with 8 ml of distilled water in a 15 ml pointed centrifuge
tube. The suspension was filtered through two layers of cheese cloth. The
filtrate was resuspended in 8 ml cf distilled water and centrifuqed for 130
seconds at 2400 rpm (including 30 seconds acceleration and 10 seconds
braked deceleration). The supernatant was poured off and then resuspended
in 8 ml of distilled water. This process was repeated a total of 10 limes
or until the supernatant appeared to be clear. The sediment was finally
resuspended in 8 ml of distilled water and centrifuged for 20 seconds at a
maximum of 1000 rpm. The function of this procedure was to throw down most
of the more dense debris while retaining the Giardia cysts in suspension.
17
-------
The sediment was reprocessed (twice) to increase cyst yield while the
supernatant was collected, resuspended in distilled water and centrifuqed
for 130 seconds at 2400 rpm with the cysts concentrated in the sediment and
ready for future use.
Determination of Cyst Density
The collected sediment was suspended in 15 ml distilled water. A
0.01 ml aliquot was pipetted from the cyst concentrate and placed on a
glass slide with a drop of Luqol's iodine. The aliquot was covered by a 22
X 22 mm No. 1 coversiip. Using briaht field microscopy at 100X, all of the
cysts observed were counted. This was repeated until twelve 1.0 ml ali-
quots had been examined. The number of cysts per 1.0 ml was estimated
by the averaqe of the twelve 0.01 ml aliquots multiplied by 100. Distilled
water was added until a suspension of approximately 36,000 cysts per ml was
obtained.
Laboratory Filtering Apparatus
Giardia cysts were placed in 4.5 liters distilled water contained in a
side-arm carboy and Dumped into a water line feeding the filter by a
proportioning pump. The suspension of cysts in the carboy was placed on a
mixer until the susoension was exhausted. To reduce pressure across
the filter, a pressure reducer was placed in the line prior to the filter
holder. A pressure qauge and flow meter were installed to monitor the
filter and measure flow. Experiments were run with both 7 urn and 1 urn
orlon filters. The experimental apparatus is shown in Figure 1. The water
pressure was set to be no higher than 10 psi.
Analysis Procedure
The filter yarn was unwound from the stainless steel filter core, cut
in 4 foot lengths, end placed, with the excess water from the filter, into
a 3500 ml beaker. Distilled water and 25 ml of formaldehyde were added to
bring the volume to 1000 ml. This suspension was placed into a one gallon
paint can and mixed in a paint shaker for ten minutes. The filter material
was removed, the fluid squeezed out, and the filters discarded. The
formalin suspension from the paint can was separated into two 500 ml
aliquots, one to be processed by a Millipore filter technique and one to be
used in a algal (or Foerst) centrifuge.
HITMpore Filter Procedure
This 500 ml of homogenate was filtered by gravity through a 45 urn and
then a 30 urn porosity nylon screen. The material retained by these screens
was discarded. The homogenate was next filtered by gravity through a 7 urn
Millipore filter. The material retained in this filter was washed in a
beaker using ?. ml distilled water. Five slides (.01 ml each) of this
filter debris were examined microscopically under low and high dry power
using Lugol's iodine as a stain. The Giardia cysts recovered were counted
and the results recorded.
18
-------
Algal Centrifuge Procedure
The other 500 ml homogenate was processed through a high speed algal
centrifuge at 1000 g. The material collected in the centrifuge was
re-suspended and mixed with 2 ml of distilled water making 7 ml of sus-
pension. Fiv2 slides (0.01 ml each) were examined microscopically under
low and high dry power using Lugol's iodine as a stain.
RESULTS
Cyst recoveries for the six experiments are presented in Table 7. In
three experiments a 7 urn orlon filter ,;as dosed with 36,000, 12,000 and
6,000 cysts respectively. In the other three experiments a 1 urn orlon
filter was dosed with 40,000, 20,000 and 10,000 cysts respectively. In
each experiment half the homogenate was concentrated using the algal
centrifuge and half by the Millipore filter technique. Results from the
algal centrifuge technique were comparable to Millipore filter technique in
cysts per ml of homogenate, however in all six experiments the percent
recovery was much higher for the algal centrifuge. The actual cyst counts
per ml of homogenate were also slightly higher for the algal centrifuge.
The 1 urn filter yielded higher cyst counts than did the 7 urn filter.
A 7 urn and 1 urn orlon filter were then installed in series so that the
1 urn filter would receive effluent of the 7 urn filter. These filters
were dosed with 40,000 cysts. Sediment was processed with the algal
centrifuge technique. Recoveries were 11 cysts from the 7 urn filter and 56
from the 1 urn filter.
The filter technique was applied to 18 surface water supplies or
streams in the state (Table 8). Giardia positive filters were identified
from the cities of Sultan in Snohomish county and Dayton in Columbia
county, neither of which reported an excess number of human giardiasis
cases. Three positive filters were identified from a stream implicated in
a series of backpacker illnesses. This cluster of human cases is described
later in the human case follow-up section (Big Four Ice Caves Trail).
DISCUSSION
Percent recoveries of Giardia cysts using 7 urn and 1 urn orlon filters
were estimated using known cyst concentrations and two methods of filter
analysis. In each of the 6 experiments the algal centrifuge method gave
higher recovery percentages, in part because it produced a larger volume of
sediment material. However, even the concentrations per ml of sediment
were slightly higher for the algal centrifuge method. Both analysis
procedures produced higher recoveries with the 1 urn orlon filter than with
the 7 urn filter. When the 7 urn and 1 urn filters were connected in series,
more cysts were detected on the smaller porosity filter. This suggests
failure of the 7 urn filter to retain significant numbers of cysts and
indicates that a smaller porosity filter should be used to recover Giardia
from water samples.
19
-------
Application of the filter to 18 water supplies or water sources
detected only two with Giardia cyst contamination. Since approximately 18%
of beaver and 33% of muskrat were found to excrete Glard'ia during earlier
stool surveys, and since Giardia positive animals were distributed through-
out the state, failure to detect more than 2 of 18 systems tested as
Giardia contaminated was unexpected. Perhaps Gi ard i a cysts are seldom
found in concentrations necessary to assure detection.
To estimate ranges of possible cyst concentrations in natural set-
tings, cyst density calculations based on Giardia prevalence among beaver,
cysts/gram of stool in positive beaver, total stool output and total water
flow were made for three locations in each of two watersheds (Cedar and
Upper Yakima). Beaver population estimates were based on Dept. of Game
trapping data for these watersheds (assuming a 10% harvest and 50% report-
ing of harvest). Stream flows were based on high, low and mean flow
measurements of the U.S.G.S. Giardia prevalence (15.8% - Cedar River,
26.3% - Upper Yakima River) and cyst density/gram stool (2/gm - low,1599/gm
- mean, 16,900/gm - high) were based on beaver stool survey results.
Total daily stool output per beaver was assumed to be 100 grams.
The results of the calculations are as follows:
Max.flow, Min cysts Min flow, Max cysts
Cedar River Watershed
Upper .0000014 cysts/gal. 5.59 cysts/gal.
Taylor Creek .0000048 cysts/gal. 245.22 cysts/gal.
Landsburg .0000093 cysts/gal. 1.34 cysts/gal.
Upper Yakima Watershed
Martin Creek .0000053 cysts/gal. .98 cysts/gal.
Cle Elum River .0000021 cysts/ga]. .35 cysts/gal.
Cle Elum City .0000015 cysts/gal. 9.71 cysts/gal.
These crude calculations suggest that cyst density only rarely reaches
levels which are detectable by current water filtration technoloc.-, pos-
sibly explaining the poor cyst recovery results with the orlon filter.
However the results of both the experimental analysis and field
application suggest that the 7 urn orlon filter can be useful in an outbreak
investigation, even if not sensitive enough for routine monitoring of water
supplies. Although the 1 urn improves recovery, insufficient field exper-
ience is available to determine the operational significance of this
improvement.
20
-------
__ PtHP
OUTLET
LINE
ro
CARBBOY
o
m
o
o
CD
o
O «-i
-< tn
o
m
FILTER CASE
ORION FILTER
-------
TABLE 7. CYST RECOVERY BY TECHNIQUE AND FILTER PORE SIZE
Cysts dosed
Filter size
Sediment vol .
Cysts recovered
per 1/100 ml *
Total cysts
recovered **
% Recovery
Cysts dosed
Filter size
Sediment vol .
Cysts recovered
per 1/100 ml
Total cysts
recovered
% Recovery
36,000
7 um
7 ml
31
4200
11.5%
40,000
1 um
10 ml
49
. 10,000
25%
12,000
7 um
7 ml
14
1960
16.0%
20,000
1 um
18 ml
19
7,200
36%
6,000
7 un
7 ml
3
420
7.0%
10,000
1 um
18 ml
7
2,520
25%
36,000
7 um
2 ml
28
1120
3.1%
40,000
1 Ul
10 ml
41
8,000
20%
12,000
7 um
2 ml
12
480
4.0%
20,000
1 um
18 ml
8
36,000
18%
6,000
7 um
2 ml
1
40
7%
10,000
1 um
18 ml
3
1,080
10%
* Estimates based on at least five 1/100 ml samples examined
** Based on cysts per ml and total sediment volume
-------
TABLE 8. RESULTS OF FIELD APPLICATION OF ORLON FILTER
SOURCE
Lake What com
Ryderwood-stream
Ryderwood-stream
Lake Whatcom
Lake Whatcom
Lake Whatcom
Lake Whatcom
Lake Whatcom
Lake Whatcom
Ryderwood
Lake Samish
Lake Whatcom
lloqui am
Hoquiam
Hoqui a-n
Hoquiam
Centralia
Centralla
Sequim
Sequim
Sequim
Sequim
Port Townsend
Port Townsend
Port Townsend
Port Townsend
Mrs. Theirs
Camas
Cam as
Stevenson
Stevenson
White Salmon
White Salmon
Carson
Carson
Camas
Carson
Carson
Camas
Stevenson
White Salmon
Stevenson
Hoquiam
*
TREATMENT
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
DATE
11-30-78
12-53-78
12- 3-73
12-13-76
12-13-78
13-14-78
12-14-78
12-14-78
12-19-78
12-26-78
1- 2-79
1- 2-79
1-30-79
1-30-79
1-24-79
1-22-79
1-29-79
2- 1-79
2- 8-79
2- 7-79
2- 6-79
2- 5-79
2- 5-79
2- 6-79
2- 7-79
2.14-79
2-14-79
2-28-79
2-27-79
2-26-79
3- 1-79
2-27-79
2-28-79
2-28-79
3-14-79
3- 1-79
2-26-79
3-20-79
3-21-79
2-28-79
3- 1-79
3-27-79
4-11-79
GALLONS
480
599
465
<500
<500
<500
<500
396
<500
<500
475
501
213
206
194
241
517
146
546
683
645
261
454
580
592
477
<500
464
491
466
575
613
602
513
454
607
476
666
447
557
607
468
475
t m
FINDINGS
Neq
Neq
Neq
Neq
Neq
Neq
Neq
Neg
Neq, Hookworm lar
Neg
Neq, Hookworm Tar
Neg
Neg, Hookworm lar
Nea, Hook worm lar
Neq, Hookworm lar
Neq
Neq, Hookworm lar
Neq, Hookworm lar
Neq
Neq, Hookworm lar
Neq
Neq
Neg, Hookworm lar
Nea
Neq
Neg
Neq, Hookworm lar
Neq, Hook worm lar
Neq, Hookworm lar,
ascaris eqqs
Neq
Neq
Neq
Neg
Neg
Neq
Neg
Neq, Hookworm lar
Neq
Neq
Neq, Hookworm lar
Neq
Neg
Neq
• »
(continued)
23
-------
TABLE 8. (continued)
SOURCE
Hoquiam
Aberdeen
Aberdeen
Hoquiam
Hoquiam
Hoauiam
Hoquiam
/•oerdeen
Aberdeen
Sultan
Everett
Everett
Sultan
Snohomish
Sultan
Snohomish
Shohomish
Everett
Everett
Sultan
Granite Falls
Granite Falls
Granite Falls
Granite Falls
Walla Walla
Walla Walla
Walla Walla
Walla Walla
Walla Walla
Dayton
Dayton
Day ton
Daytoi
Dayto'-
TREATMENT
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
DATE
GALLONS FINDINGS
4-12-79
4- 9-79
4-12-79
4-10-79
4-11-79
4-12-79
4- 9-79
4-11-79
4-10-79
4-16-79
4-16-79
4-19-79
4-19-79
4-19-79
5- 1-79
4-18-79
4-18-79
4-18-79
4-18-79
4-18-79
7- 5-79
7- 5-79
7-10-79
7-10-79
7- 2-79
7- 5-79
7- 1-79
7- 5-79
7- 5-79
7-13-79
7-11-79
V-12-79
7-14-79
7-14-79
— ... "... ii
612
47
361
236
620
606
573
361
360
631
555
546
750
508
639
500
569
409
471
330
<500
<50C
475
392
475
580
406
542
510
<500
<500
<500
<500
<500
Neq
Neq. Hookworm lar
Neg
Neq, Hookworm lar
Neq
Neq
Neq
Neq, Hookworm lar
Neg
Neg, Hookworm lar
Neq
Neg
Neg
Neg, Hookworm lar
Pos-Giardia
Neg
Neq
Neg
Neg
Neg
Pos-Giardia
Pos-Giardia
Pos-Giardia
Neq
Neq
Neq
Neg, diatoms
Neg, diatoms
Neq, diatoms
Pos-Giardia
Neq, diatoms
Neg, diatoms
Neg, diatoms
Neg, diatoms
Treatment orovided to the sample - not necessarily the system
24
-------
SECTION 6
CASE FOLLOI.-UP AND CASE CONTROL STUDY
Having established the potential for Giardia contamination of water
supplies by infected aquatic mammals, interest centered on whether human
giardiasis was associated with domestic surface water supplies. In addi-
tion, should water supplies not be a primary contributor to an increased
risk of ciiardiasis, iaentifyinq factors responsible for the hinh prevalence
of Giardia found in diagnostic stool specimens was a secondary objective.
To Identify giardiasis outbreaks as well as to determine whether
an excess number of laboratory confirmed qiardiasis cases were occurring
in cities served by surface water supplies, 3 statewide case follow-up
proqram was initiated in June 1978. By August 1978, 103 laboratories
had been contacted and statewide reporting had bequn. To identify risk
factors for giardiasis, a case-cont:%ol study was begun in March 1979. Both
the statev/ide follow-uo and the case-control study were concluded on March
1, 1980.
METHOPS
All clinical diagnostic laboratories providing parasitoloqical
services 1n Washington State were identified and asked to submit to the
State Public Health Laboratory the patient and physician name of all
confirmed qiardiasis cases identified during the study period (June 1978
to March 1980). Of 103 laboratories providing parasitological services,
03 agreed to participate in the study. Based on workload estimates,
the participating laboratories accounted for 96% of parasitological exam-
inations statewide. Alternatively, assuming an estimated stool positivity
of 3.3% (the average positivity seen in several large reporting lab-
oratories) the reported cases accounted for 65/6 of the cases which may have
been expected (by applying 3.3% positivity to the total laboratory work-
load).
There were 1241 reports of laboratory confirmed qiardiasis from
diagnostic laboratories durinq the study period. Persons were excluded
from the study if they were non-residents (16 cases), migrants (161
cases), or recent immigrants (187 cases). Of the 877 eligible cases
99 could not be found or contacted for a variety of reasons. The physician
was contacted prior to interviewing the patient and the physician recom-
mended aqainst contacting the patient in 8 cases. In another 5 cases the
patient refused to be Interviewed. A total of 765 cases (87% of eligible
cases) vere followed.
25
-------
nurinq the period of the case-control study (Marcn 1, 1979 to M*rrh
1, 1980) 488 of the 765 cases were followed. Since controls were to be
selected from directory assistance listings, cases were excluded (from the
488 followed) if they did not have a listing. There were 113 persons
excluded for this reason with 34 having unlisted telephone numbers, 18
having no phone, 41 with a phone under another name (e.g. dormitory) and 20
with no explanation cor being unlisted.
Controls were selected from the same phone book as th.» cases by
randomly choosing a oage and a name from the page, or from directory
assistance by prompting a name not listed in the ohone book but similar
to a randomly selected directory assistance name. The proportion of
controls selected in the latter fashion was determined by the proportion
of cases with a directory assistance listing but with no phone book list-
ing. Controls were matched to the cases on the basis of sex (for cases
over age 9), age (0 to 4, 5 to 9, 10 to 29, 30 to 49, 50 to 64, and over
age 64), and location of residence (same phone book sen ice area). Con-
trols were followed as soon after the case report as possible to avoid
seasonal differences in the responses of cases and controls. Of the 375
cases eligible for inclusion, 349 were actually matched within 2 months of
the report. The remainder of cases were excluded from the case-control
study.
Both cases and controls were asked about ili-^ss histories. Cases
were asked a more detailed set of questions to accurately depict the
illness and to determine the interval between potential exposure and
the onset of symptoms. A number of exposure probabilities were explored
includino pets, travel (foreign, U.S., Washington State), recreation,
residence history, domestic water supply, waste treatment and family
characteristics. Questions were also included on the use of restaurants,
occuoation and the number of bathrooms in the home. The latter two gues-
tions were used to help ascertain the economic status of the people inter-
viewed. Access to medical care was m*>?.sured oy the interval since the last
routine physical examination and interval since the last physician visit
for a problem other than giardiasis. The case and control interview
forms are included in appendix A.
RESULTS
Case Clusters
Cases often appeared in clusters. These clusters were composed of
people who shared a common exposure or who had been exoosed to another
positive person.
Several of the clusters each involved many people. There were 10
reported cases where the people had consumed water from a stream while
hiking. The stream water was later found to be contaminated by Giardia,
possibly of animal origin. Fourteen cases had a common exposure to a
Forest Service work camp. All had consumed water taken from a strean which
was later found to be contaminated with Giardia cysts. There were 11 cases
26
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which were exposed through a community water system, 12 cases which had
recently returned from Puerto Vallarta, Mexico, 17 cases from one day-care
center, and 8 from another. These will be discussed later.
The remaining 76 clusters were composed of 7 or fewer people account-
ing for 205 cases or an average of 2.6 cases per group. Twelve of the
qroups (33 cases) were composed of people who had traveled together to
foreign countries. One foreign country case was associated with 2 non-
traveling family members who became Giardia positive after her return
home, twenty of the qroups (43 cases) were composed of people who had
consumed untreated water in Washington while on an outing as a group or
during their work (loggers, game wardens, campers, etc.). In 12 of the
clusters only 1 person in each cluster drank untreated water, but a total
of 29 cases were involved. The 17 cases not exposed to untreated water
were diagnosed after the index case for the group (the person exposed to
untreated water). Persons in 2 groups (4 cases) volunteered that they
were homosexuals. One group (4 cases) was from a school for emotionally
disturbed children.
In 10 of the groups (24 cases) 13 children had attended a nursery
school or day-care home (10 different locations). Associated with the^e
13 children were 7 G iard ia lamblia positive adults, 2 Giardia lamblia
positive siblings and 2 positive piaymates.
The remaining 21 qroups involved 73 cases. Fifteen of the 21 groups
(51 cases) were composed of 1 or more positive adults and 1 or more pos-
itive or non-positive children. Of these 15 g-oups, 12 (80%) had a child
two years or younger, 9 (60%) had a child age three to five years, 8 (53%)
had a child age six to eight years, and 4 (29%) had a child age nine to ten
years. Of the 51 cases, 14 were aged two years or younqer, 7 aged three to
five years, 7 aged six to eight years, 1 aged nine to ten years, 1 aged
eleven to nineteen years, and 21 were over the age of nineteen. Of the 21
adults from these clusters (over age nineteen), 13 were female and 6 were
male. Four gr JDS (9 cases had no positive cases over the age of twelve.
Two groups (• -ases contained no childrenunder the age of twelve in the
family.
From the total 79 clusters of cases, 7 households had at least 1
member with a repeat positive. In 1 household, the positive people had
not been treated. In the other 6 they had been treated. In 6 of the
7 households there was a Giardia positive child age two or less, although
in 5 of these 6 households the reoeat positive was an adult.
In the 79 clusters of cases there were 34 instances of both a child
and ?.n adult diagnosed positive for Giardia. In 18 of the instance: the
adult was diagnosed first, in 7 the child was diagnosed first, and in
9 they were diagnosed at the same time.
27
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Big Four Ice Caves Trail, Snohomish County
During the summer of 1979, 10 confirmed and 7 suspected cases of
giardiasis were identified where the positive persons had a common exposure
to the Biq Four Ice Caves Trail in the Monte Cristo area of the Cascades.
Of the 17 confirmed or suspected cases, 9 were between age twenty and
twenty-nine, 5 were between aqe thirty to thirty-nine, and 3 were less than
aqe three. Seven were females and 10 were males. The dates of onset of
symptoms spanned the entire summer with the earliest onset being May 24 and
the latest being September 18. All confirmed or suspected cases drank
water from the same stream. One pet dog who also drank water from the
stream developed symptoms.
A survey of the immediate area where water was drawn revealed no
aquatic mammals. However directly upstream were a series of beaver
dams and lodges. In early August, a 500-gallon water sample of the
beaver pond was filtered through a 7 urn orlon filter. Analysis revealed
the presence of Giardia cysts in the water.
Althougn warning signs were posted by the Forest Service in August,
cases were diagnosed until September. This was possibly due to multiple
access trails to the area, not all of which could be posted.
Forest Service Outbreak Near Forks, Washington
In August 1978, a cluster of cases was noticed from a Forest Service
work camp. All of the Giardia positive persons in this cluster were
emoloyed by the Forest Service and most worked on brush clearing activit-
ies. An inspection of the camp's water supply and food service revealed no
likely sources of infection. Investigation revealed that during the month
of August, approximately 50% of the employees in this work camp developed
symptoms .suggestive of aiardiasis. Thirty-nine of the workers submitted
stool samples for diagnosis; 14 were positive for Giardia. Another 9
workers were diagnosed on the basis of their having three or more of the
following symptoms: diarrhea, flatulence, nausea, weakness, loss of
appetite, abdominal cramps and easy fatigueability.
Many of the positive people and others with diarrhea had consumed
water from rivers and streams in the area in addition to water from the
camp supply. Many had consumed water from a tanker truck while on a brush
clearing crew working near Forks, Washington. These workers used tht truck
to supplement the water brought from the camp. The tanker truck obtained
its water from a small stream in the area and was present at the work site
for purposes of fire control.
Water filtration was initiated on the stream used by the tanker
trucks. Three Giardia cysts were recovered using a 10 micron orlon filter.
In the fall of 1978, a Giardia positive beaver was trapped from the general
vicinity of the outbreak.
28
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Puerto Vallarta, Mexico
During the winter of 1979-80, 12 confirmed and 7 suspected qiardiasis
cases reported recent travel to Puerto Vallarta, Mexico. Most of the cases
were tourists who traveled to Puerto Vallarta with organized tour groups
for a one week visit. Seven of the 12 cases had stayed at the same hotel.
Illness occurred throughout the winter with the first case reporting travel
botween October 15 and 22, while the last case traveled between February 1
and 15. Seven of the cases traveled in November with 1 identified from the
trip of November 5 to 11 and 2 cases from trips during each succeeding week
in November. The problem of qiardiasis may be associated • ith a larger
problem of diarrheal diseases among travelers to Puerto Vallarta during
this time period. It was not possible to identify a common exposure which
distinguished cases from non-cases.
Boistfort Water System, Lewis County
During the fall and winter of 1979-1980, 11 cases of giardiasis
were reported from the Boistfort Valley area of Lewis County. Ten of the
cases were adults, 8 between the ages twenty and twenty-nine, and 2 over
age sixty. There was 1 positive child. Amony the adults, 4 were male and
6 were female. None of the cases reported having any foreign travel in the
two months prior to onset of symDtoms. One case drank untreated water from
a stream in the orior two months and 2 reported having gone swimming. All
of the reported cases were served by the Boistfort Water System or reported
drinking water from the system.. Nine of the cases received their water
from the system, 1 person was e visitor who became ill one week after
staying with a family served by the system, and the other person worked at
a dairy farm served by the system.
Four additional cases of giardiasis were reported from Lewis County
during the winter months, but they did not report any consumption of
water from the Boistfort water system.
A telephone survey was initiated when the diagnosed persons reported
multiple cases of diarrheal illness among family members, neighbors
and friends on the Boistfort Water System. Of approximately 443 households
on the system, 174 were interviewed and asked questions about any diarrheal
Illness, possible exposures to Siardia if they reoorted illness, and water
pressure problems in their homes.
There were 534. persons in the 174 households surveyed. In 37 house-
holds, at least 1 member had diarrhea that lasted longer than one week.
Sixty-eight people (12.7*) had giardiasis-like symptoms. Combining the
households of symptomatic persons with the households of the 11 positive
persons, 14.9% of the people interviewed wer. symptomatic or positive for
Two surrounding communities were also surveyed for diarrheal illness
during the same time period. A total of 65 households from the towns of
29
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Winlock and Pe Ell were surveyed. These included 168 persons of whom 8
(4.815) reported diarrhea lasting lonqer than one week. These symptomatic
persons came from 4 households and none reported consumption of water
from the Boistfort system.
The peak of the Boistfort outbreak appeared to have occurred during
December and January. The first diagnosed case reported onset of symptoms
as early as July, but 5 of the 11 became ill either in December or
January. The 68 surveyed cases with giardiasis-like illness reported the
month of onset of symptoms as ranqing from September through February, with
a cluster of 21 cases in December and 29 in January. The customers on fie
system were surveyed in February and the reports for onset of illness may
be somewhat inaccurate due to the length of time passed.
Water filtration efforts using 1 urn orlon filters were unsuccessful in
recovering cysts of Giardia from the Boistfort raw water. Stools of beaver
acquired from beaver ponds in the watershed were also negative for Giardia.
Considerable potential for water cross-connections were present.
Many dairy farms had dual water sources, one from the Boistfort supply
and one from wells on their property. Periods of low water pressure were
reported by customers throughout the system. Under negative pressure
conditions, cross-connections of these dual systems could have contaminated
the system or a portion of it. Cases of confirmed giardiasis and persons
with persistent diarrhea were reported throughout the area served by the
system, however, and water pressure recorders were unable to detect neg-
ative pressures at the locations tested.
Chlorine levels were increased on February 1, 1980 so that 0.6 mq/1
free available chlorine could be measured throughout the system. Pre-
viously no free chlorine could be measured at most places on the system. A
boil water recommendation was issued at the same time. As of May 1, 1980,
no further confirmed cases of giardiasis had been reported from the Boist-
fort area except 1 case whose onset of symptoms was witnin two weeks
of the chlorine residual increase and the boil water order. The boil
water order has since been lifted; however, high free chlorine levels
remain. A cross-connection control program has also been implemented,
Day Care Centers, Skagit County
In December 1978, an Anacortes physician diagnosed giardiasis as the
cause of a four-year-old child's "failure to thrive". The physician
noted that two sisters had also experienced diarrhea, abdominal pain and
nausea since November 1978. On examination they were found to be positive
for Giardia. As their mother was a licensed day-care mother, the physician
directed Rer to notify the families of the children enrolled of their
exposure to giardiasis. Subsequently, 7 additional positive children
with exposure to the day-care home were identified.
The cluster of cases from Anacortes was noted by Giardia Project
staff. The Skaqit County Health Department and the State Office of
30
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Epidemiology were notified after it became apparent from interviews with
the physician and parents that the day-care home was the common exposure.
The Skagit County oublic health nurse for the area interviewed the day-care
mother and obtained the names of children who had attended the day-care
home in the past five months and the names of children in the neighborhood
who had played with the positive cases. She arranged for family members of
the positive cases and for children exposed to the day-care home to be
tested for Giardia.
At that time, 19 children were examined for Giardia. Ten children
were found to be positive. Of these, 6 children lived in or attended the
day-care home, 3 children were neiqhbors who played with the day-care
home children, and 1 was a sibling of a day-care home child. Stool
samples submitted by adults living in ths same households as the positive
children were all negative for Giardia. Of the 10 positive children, 4
were symptomatic and 6 were asymptomatic for giardiasis.
The number of asymptomatic children involved made it difficult to
determine a possible source of infection for the outbreak. Five of the
children had picnicked often during the summer in Whatcom and Skagit
Counties and swam in several local lakes. One asymptomatic child had been
exposed to Giardia positive friends in Hawaii 11 months before the outbreak.
In the year following the investigation, 7 more children associated
with the day-care home were diagnosed positive for giardiasis. Of these, 2
children attended the day-care home, 4 were neighbor children, and 1 was a
sibling of an earlier cases.
The second day-care home outbreak was also in Anacortes and may have
been connected to the first outbreak as 2 of the children found positive
for Giardia had earlier attended the first day-care home. Eight people
were diagnosed positive for giardiasis as a result of the second investi-
gation. Seven of the cases were children who attended the home ano 1 was
a parent. Again it was difficult to determine the origin of the outbreak.
The parent was the first case diagnosed and may have been responsible for
introducing the parasite to the day-care home through her 2 children.
The 2 children who had attended the first day-care home had not been
positive when tested during the first outbreak. They may not have submit-
ted enough stool samples for adequate diagnosis at that time or they
may have acguired the parasite after being tested.
The second day-care mother was not as cooperative in providing
information to the Skagit County Health Department as the first had
been, so it was not possible to test as many children or parents as
in the first outbreak.
Case Follow-up and Case-Control Study
An effort was made to make the questions identical for cases and con-
trols. Despite these efforts, two questions appear to have been inter-
preted differently by cases and controls. These were the amount of Wash-
31
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ington State and other U.S. travel. For both questions, the controls
reported more frequent travel than did the cases. For Washington travel,
controls reported 3.5 times that of cases. For other U.S. travel, controls
reported 1.6 times that of the cases. Yet Canadian and European travel
were nearly identical and the cases reported considerably more outdoor
activity than did controls.
The differences in reported travel between cases and controls may have
been real or may have resulted from confusion on the part of controls over
the time period of interest. Unlike cases, the controls did not have a
traumatic event to define the time interval of interest. On the other
hand, cases may have under-reported travel which they felt to be unimpor-
tant or unrelated to their disease.
Answers to the remaining questions were recoded and condensed to
26 variables. Not all of these questions were risk factors of interest.
Six questions were potential confounders of risk factors and disease
while 7 questions related to potential effect-modifying conditions.
Several questions relating to income were collected as potential
confounding variables, such as the number of batnrooms and the occupation
of the person and his or her spouse. The occupations were ordered by
estimated income and the higher occupation score (the oerson or spouse) was
taken as the occupation variable. Several questions relating to medical
care were asked and recoded to give the number of months since the last
physician visit (other than for the diagnosis of giardiasis for the cases).
This was also considered a potential confounding variable.
An "effect modifying" variable should identify a subset of cases where
the effects of exposure nay be different than for the majority of the
population. This could happen here if a subset of the population had a
reduced immunity to Giardia either because of a medical condition (hypo-
gammaglobulinemia) or because of no prior infections with Giardia. The
effect or these people of a first time exposure to Giardia could be more
substantial than the same exposure for someone previously infected with
Giardia. For this reason, questions were asked on previous enteric prob-
lems and on length of residence in Weshinaton and at the current location.
Wright (10) suggested that lonq term residence in Colorado may be pro-
tective, perhaps due to prior Siardia exposure. The questions on place of
birth and length of residence should provide similar information for this
study. Since domestic water might also be a source of prior exposure, the
source and type of treatment of domestic water (surface filtered, surface
unfiltered or well) and size of system (number of connections) were also
included.
Since controls were selected from lists of ohone numbers rather than
from lists of people, family size cannot be considered a risk factor.
Larger families were over-represented in the cases because larger families
have a greater risk of at least one member becoming ill than do small
families. Yet large families have an equal chance of inclusion in the
32
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control copulation. Adjustment for family size must he made when esti-
matinq the importance of exposures related to family size.
The risk factors surveyed were exposure to household pets, outdoor
pets, restaurant visits (sit-down, fast-food) swimminq, untreated water
consumption, outdoor activity, number of classes of water consumed per day,
foreign travel, exposure to children less than aqe three, exposure to
children aqe three to ten, and attendance of nursery schools for children.
Variables were coded to provide for increasing values of the codes to
correspond to expected increasing or decreasing effects for the variable.
Thus, indoor pets were recoded so that zero was assigned to no pets and
three was assigned to the presence of young animals in the house. Code one
was assigned to a single adult indoor net and two was assigned to multiple
adult indoor pets. This coding was based on the hypothesis that young
animals excrete cysts more frequently than do older animals (9). Coding
instructions for the case-control study are presented in Appendix B.
Analysis of the Case-Control Data
There were four possible outcomes for each case-control pair on any
dichotomous exposure: (1) both the case and the control were exposed, (2)
both were unexposed, (3) the case was exposed and the control unexposed,
and (4) the case was unexoosed and the control exposed. The number of
case-control pairs falling into each of these categories were represented
as z(i,j) where i=l if the case was exposed and 0 otherwise and j=l if the
control was exposed and 0 otherwise. The four possibilities were repre-
sented as:
Control
Exposed Unexposed
Exposed 2(1,1) z(1,0)
Unexposed z(0,l) z(0,0)
To determine whether the exposure occurred more commonly than expected
among the cases, a variety of measures have been developed. The relative
risk was the most commonly used measure because it can easily be obtained
from case control studies, it approximates the ratio of the probability
of disease given exposure divided by the probability of disease given no
exposure (the odds ratio), and it occurs as a parameter in more complex
statistical models for the analvsis of case-control data. For these
reasons, considerable use will be made of the relative risk in the follow-
ing analysis.
The relative risk ( p ) is estimated from matched case-control
studies as the number of unexoosed controls whose case is exoosed (z(l,0))
divided by the number of exposed controls whose case is unexposed (z(0,l)).
33
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y = Z(1,0)/Z(0,1)
This ratio should be close to one when there is no association between
exposure and disease risk. When the exposure increases the risk of dis-
ease, the relative risk is greater than one and when the exposure is
protective, the relative risk is less than one. Note that the number of
case-control pairs with identical exposure does not enter into this
calculation, although it does affect the variance of the estimates.
Relative risks are calculated for each potential risk factor, con-
founding variable, and effect-modifying variable in each of three age
groups (0-9, 10-39, and 40+ years). These estimates are given in Tables
9, 10 and 11. The confidence intervals are large sample estimates of
actual confidence intervals.
Several factors stand cut as possibly important risks. Amonq these
are foreign travel, except possibly among children, untreated water con-
sumption and nursery school exposure for children zero to nine years
old. Presence of an infant in the household may be important for cases.
under 40. Swimming has a moderately increased relative risk for each age
group.
Whether each of these factors produces an independent effect on the
risk of disease cannot be answered from the above relative risk estimates.
For example, if two activities are related, such as restaurant visits and
foreiqn travel, then both might appear as risk factors even though only
one may be related to disease. Also, another factor, such as incorr.3, may
confound a relationship as illustrated previously. Third, the impor-
tance of effect modifyino variables must also be tested.
A statistical method for coping with multivariate problems from
matched case-control studies was develooed by Breslow and others (11).
This technioue provides estimates for the risk of disease given several
exposures and adjusts for both confounding and effect modifying variables.
The contribution of a risk factor can be tested as twice the differ-
ence between the log-likelihood of the equation when the factor is present
and the loo-likelihood when the factor is absent (and all other variables
are the same). This difference has a Chi-squared distribution with one
degree of freedom (approximately). For a more detailed account of the
technique and its mathematical derivation, see (12).
A computer program for performing this anal/sis was developed by
Kathv Halverson and modified by Brian Plikaytis of the Center for Disease
Control. The program was further modified for this study and adapted to a
Univac 1182.
Risk factors which had a relative risk for giardiasls significantly
different from one were combined with other potentially important variables
(confounding and effect modifying) to produce a multivariate logistic
regression equation which predicts the probability of disease. Each factor
34
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was then removed one at a time and the chanqe in the loq-likelihood tested,
The estimated parameters (b. ) were also compared for the variables still
in the equation to insure that the elimination of the variable did not
substantially alter other estimates.
Once a set of factors were identified which either made a contribution
to the likelihood equation or which altered estimates when absent, each
variable not in the equation was added one at a time and the loqlikelihood
and b.'s tested to see if the variable made a contribution.
TABLE 9. RELATIVE RISK ESTIMATES - 87 CASES AGE 0 to 9
(unadjusted)
Exposure
Years at present residence
Washinqton residence
Place of birth
Previous enteric rroblem
Fanily size
Occupation
Number of bathrooms
Months since lait M.O. visit
Indoor pets
Pet sleeoirm place
Outdoor animals
Infant in household
3-10 year old in household
Nursery school
Sit-down restaurants
Fast-food restaurants
Foreiqn travel
Swimminq
Untreated water
Outdoor activity
Number of qlasses of water
Domestic water
Aqe
Estimated
Relative Risk
1.00
.79
1.21
.83
1.34
1.04
1.32
1.94
1.19
1.04
.64
2.42
1.62
Lower/Upper 959»
Confidence Interval
3.
1.
.50
.41
.69
3.00
1.53
10.60
.91
1.44
.75
8.83
.77,
.57,
(.70,
(.42,
(1.01,
(.88,
.89,
(1.4,
(.85,
.81,
(.28,
(1.27.
(1.06,
(1.56,
.72,
.45,
.31,
(1.02,
(2.51,
(.50,
.91.
.46,
(2.71,
1.30)
1.09)
2.10)
1.75)
1.77)
1.24)
1.95)
1.21)
1.65)
1.34)
1.49)
4.58)
2.47)
7.68)
2.76)
1.06)
28.80)
2.29)
44.86)
1.67)
2.26)
1.21)
28.80)
35
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TABLE 10. RELATIVE RISK ESTIMATES - 180 CASES AGE 10 to 39
(Unadjusted)
Exposure
Estimated
Relative Risk
Lower/Upper 95*
Confidence Interval
Years at preser.t residence
Washinqton residence
Place of birth
Previous enteric problem
Family size
Occupation
NuTiber of bathrooms
Months since last M.D. visit
Indoor pets
Pet sleepinq place
Outdoor animals
Infant in household
3-10 year old in household
Sit-down restaurants
Fast-food restaurants
Foreign travel
Swimming
Untreated water
Outdoor activity
Number of glasses of water
Domestic water
.99
.94
16
11
28
02
31
1R
.91
1.04
.55
2.46
1.95
1.12
1.00
10.33
1.68
7.13
.90
1.12
.86
(.88, 1.11)
(.83, 1.05)
(.83, 1.61)
(.71, 1.71)
(1.07, 1.53)
.91, 1.16)
.97, 1.76)
(.94, 1.47)
(.72, 1.14)
(.54, 1.31)
(.26, 1.20)
(1.43, 4.23)
(1.32, 2.88)
(.80, 1.57)
(.73, 1.38)
(3.16, 33.79)
(1.28, 2.22)
(3.68, 13.80)
(.58, 1.40)
(.85, 1.46
(.60, 1.21
36
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TABLE 11. RELATIVE RISK ESTIMATES - 82 CASES OVER AGE 39
(Unadjusted)
Estimated Lower/Upper 95%
Exposure Relative Risk Confidence Interval
Years at present residence .91 (.77, 1.08)
Washinoton residence .96 (.79, 1.17)
Place of birth .61 (.34, 1.09)
Previous enteric problem .70 (.39, 1.27)
Family size 1.24 (.92, 1.68)
Occupation .80 (.66, .97)
Number of bathrooms 1.22 (.82, 1.81)
Months since last M.D. visit 1.21 (.85, 1.72)
Indoor pets .93 (.64, 1.35)
Pet sleeping place 1.01 (.73, 1.40)
Outdoor animals 1.00 (.14, 7.10)
Infant in household 1.34 (.29, 6.14)
Sit-down restaurants .84 (.53, 1.31)
Fast-food restaurants 3.22 (1.40, 7.42)
Foreign travel 6.00 (1.77, 20.36)
Swimming 2.38 (1.31, <.32)
Untreated water 3.61 (1.48, 8.79)
Outdoor activity 2.74 (1.22, 6.18)
Number of qlasses of water 1.35 (.92, 1.97)
Domestic water 1.17 (.67, 2,02)
37
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TABLE 12. MULTIVARIATE EQUATIONS
FACTOR
0-Q Year Old Cases -
Untreated water
Nursery school
Swimminq
Infant in household
Foreign travel
Sex
AOP
Family size
10-39 Year Old Cases
Foreiqn travel
Untreated water
Infant in household
Indoor oets
3-10 year old in
household
Swimminq
Familv size
Aqe
Sex
40+ Year Old Cases -
Foreiqn travel
Swimminq
Untreated water
Outdoor activity
Place of birth
Number of fast-food
restaurant visits
Years at present
residence
RR*
R7 Cases
43.3
5.7
1.7
2.7
1.5
.6
.1
1.3
- 180 Cases
14.9
5.0
2.8
.8
1.9
1.4
1.0
.8
82 Cases
14.1
2.0
.6.9
5.5
.4
2.6
.7
2
X, , P*
22.6 (D <.0005)
10.1 (p <.005)
2.3 (D >.l)
3.6 (p <.l)
.1 (P >.l)
1.0 (p >.l)
16.4 (p <.0005)
1.3 (p >.l)
24.3 (p <.0005)
37.6 (p <.0005)
8.8 (p <.005)
2.3 (D >.l)
3.9 (p <.05)
2.6 (p >.l)
.1 (o >.l)
.9
.1
14.1 (p <.0005)
2.3 (p >.l)
12.8 (p <.0005)
9.0 (P <.005)
3.5 (p <.l)
3.9 (p <.05)
6.5 (p <.025)
C.I.*
(4.8, 387.6)
(1.7, 19.7)
(.8, 3.3)
(.9, 7.8)
(.1, 19.7)
(.2, 1.8)
(0.0, .5)
(.8, 2.0)
(3.8, 59.2)
(2.7, 9.4)
(1.3, 5.7)
(.6, 1.1)
(1.0, 3.6)
(.9, 2.0)
.8, 1.4
(.5, 1.3)
(2.5, 80.0)
(.8, 5.0)
(1.9, 24.8)
(1.5, 19.2)
(.2, 1.1)
(.9, 7.4)
(.6, .9)
(continued)
38
-------
TABLE 12. (continued)
y2
'•! = 2 (loglikelihood with factor - loglikelihood without factor)
P = probability associated with the Chi-squared value
R.R. = estimated relative risk exp (Bk)
C.I. = 95% confidence interval based on variance estimates derived
from the inverse of the Fisher Information Matrix
TABLE 13. RELATIVE RISK ESTIMATES - 87 CASES AGE 0 to 9
(Adjusted*)
Exposure
Estimated Relative Risk
Unadjusted Adjusted
X2 P
"i »r
Lower/Upper 95%
Confidence
Interval*
Years at present residence
Washington residence
Place of birth
Previous enteric problem
Family size
Occupation
Number of bathrooms
Months sincft last M.O. visit
Indoor pets
Pet sleeoing place
Outdoor animals
Infant in household
3-10 year old in household
Nursery school
Sit-down restaurants
Fast-food restaurants
Foreign travel
Swimming
Untreated water
Outdoor activity
Number of glasses of water
Domestic water
1
1
1
1
1
1
1
1
2
1
3
1
3
1
10
1
.00
.79
.21
.83
.40
.04
.32
.94
.19
.04
.64
.42
.62
.50
.41
.69
.00
.53
.60
.91
.44
.75
1.16
1
•
07
1.75
1
•
•
97
28
0
1
0
1
1.04
2
1
1
2
1
5
1
1
1
43
4
1
•
.
•
•
•
•
•
•
,
•
•
•
»
•
•
•
88
24
11
95
60
68
67
74
24
74
45
67
33
42
76
57
5
3
10
2
22
3
2
1
.4
.0
.1
.0
.3
.1
.1
.1
.1
.1
.4
.6
.8
.1
.2
.9
.1
.3
.6
.9
.4
.9
(P
(P :
(P :
(p
(P
P :
P
(p
(P:
(P
(P
(P
(P
(p
(P
(P
P
(P
(P
(P
(P
(P
>.D
>.D
>.D
>.D
>.D
>.D
>.i)
<.05)
>.l)
>.D
>.D
<.D
>.D
<.005)
>.l)
>.l)
>.l)
>.l)
<.0005)
<.05)
>.D
>.l)
(.72,
(.56,
(.58,
(.32,
(.82,
(.79,
(.44.
(1.01,
(.85,
(.63,
(.36,
(.93,
(.55,
(1.67,
(.43,
(.39,
.11.
(.85,
(4.84,
(.88,
(.82,
(.26,
1.88)
2.04)
5.35)
2.93)
2.00)
1.37)
1.78)
4.97)
1.65)
1.43)
7.16)
7.77)
5.11)
19.74)
3.6u;
1.40)
19.70)
3.28)
337.60)
22.22)
3.78)
1.27)
*Adjusted by a logistic model with factors given 1n Table 11
39
-------
TABLE 14. RELATIVE RISK ESTIMATES - IRQ CASES AGE 10 to 39
(Adjusted*)
Estimated Relative Risk X* ,P Lower/Upper 95%
Exoosure Unadjusted Adjusted Confidence Interval*
Years at present residence
Washington residence
Place of birth
Previous enteric problem
Family size
Occupation
Number of bathrooms
Months since last M.D. visit
Indoor pets
Pet sleeping place
Outdoor animals
Infant in household
3-10 year old in household
Sit-down restaurants
Fast-food restaurants
Foreign travel
Swimming
Untreated water
Outdoor activity
Number of glasses of water
Domestic water
.99
.94
1.16
1.11
1.28
1.02
1.31
1.18
.91
1.04
.55
2.46
1.95
1.12
1.00
10.33
1.68
7.13
.90
1.12
.86
1.03
1.12
.82
.78
1.03
1.06
1.08
1.35
.79
.97
.58
2.75
1.88
.99
1.13
14.93
1.35
5.03
.54
1.09
.85
.1 (p >.l) (.87, 1.22)
1.7 (p >.l) (.94, 1.34)
.5 (p >.l) (.49, 1.37)
.6 (D >.l) (.42, 1.46)
1.1 (D >.l) (.76, 1.40)
.4 p >.l) .89, 1.25)
.1 (D >.l) (.70, 1.66)
3.6 (p <.l) (.98, 1.84)
2.3 (p >.l) (.57, 1.10)
0.0 (p >.l) (.68. 1.37)
.9 (p >.l) (.19, 1.76)
8.8 (p <.005) (1.32, 5.71)
3.9 (P <.05) (.99, 3.60)
0.0 (p >.l) (.63, 1.55)
.4 (p >.l) (.74, 1.74)
24.3 (p <. 0005H3. 76, 59.24)
2.6 (p >.l) (.93, 1.97)
37.6 (p <.0005)(2.68, 9.43)
3.2 (p <.l) (.28, 1.07)
.2 (p >.l) (.76, 1.58)
.4 (p >.l) (.52, 1.40)
*Ad.iusted by a loqistic model with factors given in Table 11.
40
-------
TABLE 15. RELATIVE RISK ESTIMATES - 82 CASES OVER AGE 39
(Adjusted*)
Estimated Relative Risk x* ,P Lower/Upper 95%
Exposure Unadjusted Adjusted Confidence Interval*
Years at present residence
Washington residence
Place of birth
Previous enteric oroblem
Family size
Occupation
Number of bathrooms
Months since last M.D. visit
Indoor pets
Pet sleeoinq place
Outdoor animals
Infant in household
3-10 year old in household
Sit-down restaurants
Fast-food restaurants
Foreign travel
Swimming
Untreated water
Outdoor activity
Number of glasses of water
Domestic water
.91
.96
.60
.70
1.24
.80
1.22
1.21
.93
1.01
1.00
1.34
1.00
.84
3.22
6.00
2.38
3.61
2.74
1.35
1.17
.75
1.01
.43
.78
1.18
.82
.66
1.09
1.03
1.01
12.76
1.56
.95
.94
2.60
14.14
1.97
6.92
5.45
1.70
.81
6.5 (p <.025) (.59, .95)
0.0 (p >.l) (.72, 1.42)
3.5 (p <.l) (.16, 1.12)
.3 (p >.l) (.33, 1.86)
1.1 (p >.l) (.81, 1.70)
1.6 (p >.l) (.60, 1.12)
1.3 (p >.l) {.32, 1.37)
0.0 (p >.l) (.61, 1.94)
0.0 (p >.l) (.57, 1.88)
0.0 (p >.l) (.61, 1.98)
2.6 (p >.l) (.58, 283.22)
.2 (p >.l) (.20, 12.13)
0.0 (p >.l) (.29, 3.12)
0.0 (p >.l) (.49, 1.82)
3.9 (p <.05) (.92, 7.35)
14.1 (p <.0005) (2.50, 80.00)
2.3 (o >.l) (.77, 5.02)
12.8 (p <.0005) (1.94, 24.75)
9.0 (p <.005) (1.54, 19.23)
2.9 (D <.l) (.89, 3.22)
.2 (p >.l) (.33, 1.94)
*Adjusted by a logistic model with factors given in Table 11
41
-------
Separate regression equations were developed for the three aqe groups
(0-9 years, 10-39 years and 40 plus years). The estimated relative risks,
Ctrl-squared statistic for removal and p-value of the Chi-squared statist
-------
relative risks. Among children, aqe was a confoundinq variable which
significantly affected the likelihood eauation and relative risk estimates
for other variables.
Foreign travel was examined in more detail to determine the difference
between cases and controls. The foreign travel variable had been recoded
to exclude Canadian travel, which vas comparable for cases and controls.
Table 16 shows the place of travel for cases and controls. It is apparent
that cases travelled more often to countries sometimes called Third World
or Developing Countries. European travel was comparable for cases and
controls.
TABLE 16. FOREIGN TRAVEL DESTINATION FOR CASES AND CONTROLS
Destination
Frequency
Cases
TontroTs
Canada
Europe
Mexico
South nr Central America
Middle East or North Africa
Southeast Asia
Africa
Northern Asia
Multiple country
22
1
28
12
3
5
1
2
3
24
1
3
0
0
0
0
0
4
TABLE 17. RELATIVE RISK ESTIMATES CALCULATED WITH (87 CASES)
AND WITHOUT (74 CASES) THE 11 MY CARE CHILDREN
.Exposure
Untreated water
Nursery school
Swimming
Infant in household
Foreign travel
Sex
Age
Family size
Relative Risk
(87 Cases)
43.3
5.7
1.7
2.7
1.5
.6
.1
1.3
Relative Risk
(74 Cases)
22.2
4.2
1.5
1.6
.9
.3
.1
1.2
X2,P
(74 cases)
16.8 (P <.0005)
6.5 (p <.05)
1.3 (p >.l)
.7 p >.l
0.0 (p >.l)
--
12.1 (p <.0005)
.7 (p >.l)
43
-------
Biases
The methods of ascertainino cases or of selecting controls may also
affect the estimated relative risks. Two such issues are considered. One
relates to the method of ascertaininq cases amonq children attending day-
care centers and the other to the method of selecting controls for adult
cases.
Giardia infections in children who attend a day-care center may be
ascertained more completely than Giardia among other children simply
because physicians expect a relationship between nursery schools and
intestinal parasites. If so, this expectation could generate the relation-
ships observed in the data. To partially adjust for ascertainment biases,
an analysis of 74 cases which were not part of any known day-care center
outbreak were compared to their matched controls (Table 17). The esti-
mated relative risks for untreated water consumption and nursery school
exposure were reduced slightly but were still significant.
The over-representation of children in the families of adult cases may
have resulted from the over-representation of children among the cases.
The excess number of children among the cases made many control calls
necessary to obtain matches. Many of these control calls generated ooten-
tial matches for other cases in the area. However, these potential con-
trols might not have young children in the household. Some of these
controls were matched to adult cases. To determine whether the matching
process had an effect on the estimated relative risk for an infant in the
household, all control families were again examined. When a potential
match to a case in the twenty to twenty-nine years age group or the thirty
to thirty-nine age grouo was found, a tally was made for the presence of an
infant in the household. These tallies were then compared to the percent
of cases in the respective age groups with a child under age three in the
household. Excluded from the cases in this group were people with recent
roreign travel or recent consumption of untreated '/ater.
For potential controls in the twenty to twenty-nine year age group,
32.3< had a child under age three in the household. This compared with
16.3% of cases in the age group who had no foreign travel or untreated
water consumption. Among potential controls in the thirty to thirty-nine
age group, 19.8% had a child under age three while 32.0% of the cases 1n
this age group (without foreicn tra»el or untreated water consumption) had
a child under age three.
The results of this analysis suggest that the relative risk of having
an infant in the household was probably over-estimated for the enti-e age
group. There is no evidence that cases twenty to twenty-nine with a child
in the household have an increased risk of giardiasis.
Comparison of Cases Matched and Unmatched
The exclusion of persons without a phone, with unlisted phone numbers
or with group residences was necessary to insure that cases and controls
were comparable (that is, drawn from the same population). The exclusion
44
-------
of these cases mav reduce the estimated importance of risk factors which
occur more comironly among peoole excluded. To determine if this had
happened and to identify risk factors which differ between matched and
unmatched cases, a comparison of characteristics of cases matched and cases
not matched was done.
For each of the 23 items used in the analysis of the case-control
study and for three items relating to characteristics of the domestic water
supply of cases, a Chi-squared statistic was calculated to determine if
the factor had a comparable distribution for matched and unmatched cases.
The results of the tests are given in Table 18.
Since the age distribution was demonstrated to be different for
matched and unmatched cases (p < .001), a comparison of characteristics
within aqe groups was done (aqe groups 0-9, 10-39, 40+). Thirty-seven
percent of the unmatched cases were under age ten while 25% of the matched
cases were under age ten.
As expected, the length of time at the present residence differed
for matched and unmatched cases for each of three aqe qroups considered
(age 0-9, p = .016; aqe 10-39, o = .000; aqe 40+, p = .036). In each age
qroup the proportion of unmatched cases residinq at the current residence
for one year or less was greater than the proportion of matched casas
(59% vs. 47%, 72% vs. 42%, and 25% vs. 13% for the three respective age
croups). The total duration of residence in Washington did not differ for
unmatched and matched cases after adjusting for the aae differences between
the matched and unmatched cases.
No other differences were observed uniformly across all age groups.
For the ten to thirty-nine aqe group and the forty plus aqe qroup, dif-
ferences in the number of sit-down restaurant visits per week (p =.017 for
10-39 year old cases, D =.0025 for 40+ year old cases) and the number of
fast food restaurant visits per week (p =.062 for cases 10-39 years old; o
= .009 for cases 40+) were observed. For both age qroups, the unmatched
cases visited more restaurants.
For the 10-39 year group, differences in the number of glasses of
water oer day (p =.011), swimminq (p =.023), occupation (p =.003), infant
in household (p =.045), outdoor activity (p =.046) and number of bathrooms
(p =.000) were observed. The matched cases drank more water, went swimming
less often, were more often from a professional or managerial occupation
group, had fewer infants in the household, had more outdoor activities and
more bathrooms in their homes.
An analysis was done on the reasons for non-matching. In 34 cases
the person had an unlisted number. In 18 cases there was no phone. In
41 cases the phone was listed under someone else's name or under a group
residence name such as a dormitory. In 26 instances the case was match-
able, but a match could not be obtained within the seasonal constraints.
In 20 instances there was no phone listing in directory assistance and no
explanation could be obtained. In each of these instances the case did
45
-------
have a phone.
The length of residence in Washington was shorter for cases with no
phone than for other cases. No difference in length of Washington resi-
dence was observed for the other groups. The length of time at the present
residence was comparable for matchable people and for people with unlisted
phone numbers but was over one year shorter on the average for other groups
(p =.04). The occupation status (based on the artificial scale in Appen-
dix C) showed that persons with unlisted phones had a higher score than
matchable cases and that persons with no phone had a lower score. As
mentioned earlier, when these groups were combined, the qroup of unmatched
cases (as a whole) had a comparable occupational distribution to that of
matched cases.
The aqe distribution for unmatched cases also differed by reason for
non-matchinq (p =.04). Fewer children were observed in the qroup of cases
with phone listings under another name and where the phone number was
unlisted for no apparent reason.
TABLE 18. MATCHED VS. UNMATCHED CASES
RISK
Sex
Aqe
Famil
Wash.
FACTOR
v size
resident
Present resid.
Indoor pets
Foreign travel
# of
1 of
glasses
sit-down
restaurants
ALL CASES
x?=
Ps
v'_
P"
2 _,
XP=
x2=
p=
xf-
p*
V2
Xls
P=
0=
x?«
p=
x!-
p=
20
6
13
70
1
14
14
.2
.1
.7
.3
.5
.8
.0
.1
.1
.647
.001
.250
.065
.000
•
.848
.321
.007
.003
0-9 YEAR
0
1.0
1.8
.184
7.9
.096
10.2
.069
13.9
.016
.2
.930
1.4
.239
7.5
.111
3.9
.268
10-39
3.
•
4.
5.
38.
1.
1.
13.
YEAR
1
4
4
9
4
4
2
0
.077
.504
.496
.555
.000
.708
.265
.011
10.2
.017
40+ YEAR
2.2
0
1
9.2
9.5
15.0
1.2
0
1
5.7
14.3
.142
.0
.100
.211
.036
.752
.0
.125
.002
(continued)
46
-------
RISK FACTOR
# of fast food
restaurants
Swimminq
Untreated water
Occupation
Place of birth
Infant in
household
3-10 year old
in household
Months since
last M.D. visit
Previous enteric
problem
GUrdia
contact
Pet sleeping
place
Outdoor
animals
Outdoor
activity
# of bathrooms
Nursery school
exposure
Surface
unfiltered
TABLE 18
ALL CASES
X'= 11.7
p= .011
Xj« 5.3
p= .070
X*= .614
pa .433
p--. ' .000
X*= 1.82
p= .610
X?" 2.01 '
p= .366
X?» 7.65
D- .022
Xj= 1.39
p= .707
X?« 0
p= 1.0
0= " 1.0
xf= 4.3
D« -231
xj= o
p= .958
X?= 1.4
D- .231
Xj= 29.5
p= .000
X , - 5.6
p= .182
X?= .2
D= .661
(continued)
0-9 YEAR
1.7
.637
1.6
.479
.01
.936
8.2
.147
.4
.934
.4
.821
2.9
.236
3.1
.370
0
1.0
2.4
.295
5.7
.128
.4
.518
0
.959
5.3
.152
.2
.696
.1
.769
10-39 YEAR
7.3
.062
7.6
.023
0
.963
15.6
.003
2.0
.571
6.2
.045
1.1
.566
1.0
.803
.6
.450
1.3
.513
4.1
.253
.2
.642
4.0
.046
18.4
.000
—
.3
.595
40+ YEAR
11.6
.009
.1
.955
.8
.378
8.2
.147
.9
.651
0
1.0
1.3
.523
1.2
.752
0
.880
.3
.874
1.2
.746
1.4
.235
0
1.0
4.4
.111
—
.6
.441
47
-------
An Examination of Cases Without Apparent Exposures
The analysis of case clusters and the case-control study identified
several exposures which appear to place the individual at an increased
risk of qiardiasis. The exposures include drinkinq untreated surface water
within two months of symptoms onset, foreign travel within two months of
symptoms onset, attendance at a day-care center (for children) and likely
secondary transmission where the index case had one of these exposures.
An examination of all cases followed reveals that 323 of the 7f-5 cases
(4230 consumed untreated surface water within two months of symptoms onset
and that 146 of 765 cases (19%) had recently travelled to a foreign country
(other than Canada). Among chi.dren less than aqe six, 84 of 113 cases
(74515) attended a day-care center. (For 43 children day care centar atten-
dance was unknown.)
Removinq these people and positive persons with exposure to one of
these people and persons identifying themselves as homosexuals leaves 207
of the original 765 cases (27%). There are 108 males and 99 females in
this grouo. The aqe distribution shows an excess number of cases in the
0-4, 20-29 and 30-39 year aqe groups (Table 19).
The presence of an infant in the household was examined by the aqe and
sex of the case (Table 20). The percent of persons in this group who were
20-29, and 30-39 with an infant in the household was compared to the
percent expected for the age group. For the 20-29 year old cases, the
observed and expected percents were nearly identical, while for the 30-39
year old cases the percent observed was nearly twice that expected (Table
21). This result is in general agreement with that of the case-control
study which considered matched cases followed during a 12 month period
rather than cases without other exposures followed durinq the total
20 month period of the project. These results cannot be considered to be
completely independent, however, because of some overlap in cases.
Swimming was also a common exposure among these cases. Thirty-nine
percent of the males and 53% of the females reported swimming within two
months prior to the onset of symptoms. Over half of the swimming was done
in natural water (other than pools) (Table 22). Exposure to swimming
occurred less often between October and December of each year, but other-
wise showed no seasonal difference (Table 23).
The distribution of cases by source of domestic water supply did not
demonstrate a seasonal trend (Table 23) nor were there remarkable clusters
by county or by month of onset (Table 24). Most of these cases occurre-*
as isolated events with few county-month of onset cells having more than
one occurrence and few consecutive months having case reports for a par-
ticular county (except for King County).
48
-------
TABLE 19. AGE-SEX DISTRIBUTION (RESIDUAL CASES*)
Aqe
0-4
5-Q
10-19
20-29
30-39
40-59
60+
TOTAL
Male
20
5
10
32
23
10
8
108
Female
8
4
11
26
22
21
7
99
Total
28
q
21
58
45
31
15
207
* Total
14*
4*
IDS
28*
22*
15*
U
100*
1979 State
Population
7.3*
7.6*
17.5*
19.4*
14.1*
19.7*
14.6*
100.2*
*Residual cases include persons without foreign travel, untreated water
or nursery school exposure, who did not state they were a homosexual
and were not in contact with a Giardia positive child or adult.
TABLE 20. PRESENCE OF AN INFANT IN THE HOUSEHOLD
(Residual Cases)
Age
0-4
5-9
10-19
20-29
30-39
40-59
60+
TOTAL
Male
0
7
4
10
23
17
8
8
77
Cases
1
11
1
7
4
2
25
-Infants*
2 3
2
*
2
2
6
Female
0
3
2
10
16
16
21
7
75
Cases
1
5
2
1
9
2
19
-Infants*
2
1
3
4
3
1
1
*Child less than •.-e 3, other than the case.
49
-------
TABLE 21. OBSERVED AND EXPECTED INFANTS IN THE HOUSEHOLD
(Residual Cases)
Number Cases With
Child < Age 3
Age Case In Household
20-29 5B 19
30-39 45 12
Percent Total
32 M
26. n
Percent
Expected*
31.5*
13.7*
*The expected percents are based on an estimated number of births to the
current state population of females in each age class over the past three
years. This assumes that there is only one birth per woman and one woman
per household and ignores adoptions to derive an estimate of the percent
of households with a child less than aqe three. Changes in the birth rate,
multiple births to a woinan during the three years, and multiple women in
a household wouVi most likely reduce thp estimated expected values some-
what.
TABLE 22. SWIMMING BY AGE AND SEX
(Residual Cases)
0-4
5-9
10-19
20-29
30-39
40-59
60+
TOTAL
60
Males
None Pools Other
8
9
4
19
13
8
8
3
3
1
4
9
2
0
9
2
5
Q
i
0
0
22
26
Females
None
2
1
2
10
11
17
4
Pools
1
3
3
7
6
2
2
Other
5
0
6
9
5
2
1
47
24
28
50
-------
Pierce
TABLE 2'-
COUNTY BY MONTH OF ONSET {RESIDUAL CASCS)
Month of Onset
County
.,,„
1979
I960 Unknown
7 8 9 10 11 12 1 2 Month
13 . 1121
211
I 1 121
21 1
2 2
Z 1 1111 i — " "
-------
TABLE 23. EXPOSURE BY SEASON OF SYMPTOMS ONSET
(Residual Cases)
Time Period Cases
Prior to 6/78 11
6/78-9/78 54
10/78-1/79 37
2/79-5/79 27
6/79-9/79 34
10/79-1/80 28
2/80 1
Unknown 15
TOTAL 207
% Total
5%
26%
13%
16%
14%
0%
7%
99%
% of Cases With Exposure to:
Domestic
Swimming Surface Mater
64%
59%
24%
56%
50%
21%
0%
93%
48%
36%
44%
68%
63%
56%
54%
0%
47%
54%
A comparison of cases with identified exposures likely to cause the
infection and cases without such exposures shows that a similar percent of
both groups were served by surface unfiltered water supplies (Table 5-7).
Should surface unfiltered water supplies contribute substantially to the
risk of giardiasis, then the percent of cases without obvious exposures
served by surface unfiltered water supplies should have been greater. A
comparison of the exposure groups by size of the water utility (system
class) shows that a comparable percent of both groups were served by class
1 water utilities.
TABLE 25. SOURCE OF DOMESTIC WATER SUPPLY BY EXPOSURE GROUP
Source or
Type of Supply
Surface unfiltered
Surface filtered
Well or spring
Total
•
Total Cases
(765 cases)
337
69
359
765
Identified
Exposures
(558 cases)
45%
9%
46%
100%
Residual
Cases
(206 cases)
41%
10%
49%
100%
Class 1
577
73*
80%
52
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SECTION 7
DISCUSSION
The concerns which motivated this study focused on waterborne trans-
mission of giardiasis. The waterborne outbreak in Camas in 1976 and the
subsequent finding of a high prevalence of Giardia sp. infection in aquatic
mammals throughout the state (9) suggested a potential for widespread
outbreaks of giardiasis through contaminated water supplies.
Despite an intensive surveillance of laboratory confirmed giardiasis
in Washington State, only two likely waterborne outbreaks were identified.
Other exposures appeared to be more common sources of infection.
The results of the study establish thai gUrdiasis is a relatively
common parasitic infection in Washington State. Considering the difficulty
in obtaining stool samples from ill persons, problems in identification
of the parasite when an infection is present, and the potentially large
number of asymptomatic or moderately ill persons who do not submit stool
samples for analysis, the true incidence of giardiasis is likely to
be much higher than that reported here. It should also be recognized that
these unreported cases could substantially bias the results of this study.
Among cases reported, giardiasis has a bimoda1 a^e distribution
more often affecting young children and young adults. Teenagers and adults
over age 40 were represented less commonly riiong the cases than expected.
Males were affected more often than females.
The bimodal age distribution of giardiasis remains even after removing
cases with identified likely sources of infection. To what extent the age
distribution of reported cases is determined by factors affecting the onset
of symptoms rather than acquisition of infection is unclear. A larger
number of asymptomatic children were identified than asymptomatic adults,
suggesting that either more infections went undetected among children or
that the case ascertainment was better for children.
Risk factors appear to include nursery school exposure for child-
ren, foreign travel for adults and consumption of untreated water for all
age groups. The relationship between giardiasis and nursery school
exposure has recently been established (13) and was seen both in the
case-control study and in two outbreak investigations in Skagit County.
For cases over age 10, foreign travel placed the individual at an increased
risk of disease. The relationship between foreign travel and ;giardiasis
was supported by the occurrence of disease usually within one month of the
53
-------
trio and by the increased relative risk of foreign travel for cases in the
case-control study. The entire.excess of foreign travel for cases in the
case-control study resulted from travel to Third World countries.
Consumntion of untreated water was an important risk factor for all
aqe qroups. Over 40^ of the cases had recently consumed untreated water.
This exposure occurred more commonly among adult males, but was observed
in both sexes and in all age groups. It occurred throughout the year,
but more commonly during the summer. An examination of the place of
untreated water consumption showed that 31 of 39 counties were repre-
sented.
Evidence of secondary transmission (most likely person-to-person} was
obtained more commonly than expected. The literature provides few examples
of secondary transmission of Giardia. Although it is impossible to con-
clusively establish that secondary transmission occurred, the later occur-
rence of ojiardiasis among family members of an index case and the failure
to find exposures of significance among anv members of the family other
than the index case is suggestive of secondary transmission. If these
families are examples of secondary transmission, then disease was spread
from adults to children, from children to adults and between adults.
The role of children in the household appeared to be important for
cases age 10-39 years from results of the case-control study, but this
may have been an artifact of the control selection procedure. When com-
pared to all potential controls, rather than the controls matched to cases,
no excess of infants was observed for cases age 20-29. A higher level
of exposure to children under age three was observed for cases age 30-39
when compared to all potential controls or when compared to an exoected
level of exposure for the population (based on the number of births to
women in this age group). Why an excess should occur for one ege group and
not for another is unclear.
The occurrence of giardiasis case clusters among groups of children
may support the role of children in the secondary transmission of giardi-
asis or may simply be related to an increased susceptibility of children to
the infection. The number of repeat positive adults with children under
age three in their household does support the role of children in trans-
mitting the disease, but the number of such cases is small. Treatment
failure rather than re-infection could explain this observation.
The role of other factors for increasing or modifying the risk of
giardiasis is, at best, less imoortant than the risk factors discussed
above. Homosexual activities were not surveyed for cases due to the
implication of even asking these questions and the limited need for the
information. Some homosexual activity was reported, however. Swimming
demonstrated a slightly increased relative risk for each age group, but was
not significant for any . je group. Outdoor activity was significant for
t-very age group, but the effect was reversed for cases over age 40 compared
to cases under age 40. For the younger cases, outdoor activity increased
the risk of giardiasis, even after adjusting for consumption of untreated
54
-------
water. For cases over age 40, outdoor activity ,-educed the risk. Since
many water supplies at recreational sites are untreated or marginally
treated, it was expected that outdoor activity would increase the risk of
giardiasis even though the case dio not report consumption of untreated
water. The results of the study do not conclusively support this hypoth-
esis.
Factors which do not predict disease or modify the effects of other
variables include place of birth and length of residence at the present
location for cases under age 40 and length of Washington State residence.
Source of domestic water supply was also unimportant in modifying the
effects of other risk factors. These results contradict the finding of
Wright (10) in Colorado where length of residence in the state predicted a
reduced risk of qiardiasis. The exclusion of controls without directory
assistance listings and the procedure of drawing controls from both direc-
tory assistance listings and from telephone books rather than strictly from
telephone books may have caused this different conclusion. Wright's study
compared laboratory diagnosed cases to controls selected from the telephone
book. Cases with or without phone book listings were matched to controls
selected from the telephone book. By selecting controls from the telephone
book, one insures a minimum residence for controls of approximately six
months. The actual minimum length of residence depends on the age of the
telephone book. This bias is amplified when a large number of people move
into an area (such as either Colorado or Washington State).
The role of domestic water supplies was examined for cases without any
of the established exposures mentioned. Of the 765 cases followed, only
207 remained after cases with foreign travel, untreated water consumption
(springs or creeks etc.), nursery school exposure, homosexuality and case
clusters where the index case had one of the above exposures were excluded.
These exposures accounted for 73% of the cases followed. The residual
cases were analyzed to determine if more than expected came from counties
served primarily by surface water supplies, whether these cases clustered
by time or by geographic location and whether they occurred more commonly
than expected from customers of surface water supplies. No evidence was
developed to support a role of surface water supplies in increasing the
risk of giardiasis. Fifty-one percent of all cases reported were served by
surface water supplies. After removing the 73* of cases with likely
sources of infection, 54X of the .residual cases were served by surface
water. These figures compare to 46% expected if statewide reporting was
uniform and there was no water supply effect.
The conclusion that no evidence was developed to support a role of
public water systems in increasing the risk of giardiasis must be qual-
ified. In one outbreak during the project period a public water system
was implicated in transmission of giardiasis. It is possible that other
outbreaks went undetected. Clearly not all giardiasis cases in the state
were identified by the project. Further there may be biases in the identi-
fication of cases which work against identifying these outbreaks. For
example, small water utilities are of special concern for the transmission
of giardiasis because their treatment facility is often both poorly equip-
55
-------
oed and inadequately operated. The customers of these utilities often have
low incomes, are isolated from access to good medical care (both physically
and financially) and are either unaware of the health department or dis-
trustful of government. Consequently, outbreaks in these populations may
be both more likelv and less detectable than outbreaks elsewhere.
56
-------
SECTION 8
HUMAN STOOL SURVEY
Since many Giardla infections are likely to result in asymptomatic
infections rather than disease, the failure to observe an increased risk
of qiardiasis among customers of surface v.ater supplies does not neces-
sarily imply that public water systems using surface water do not increase
the risk of infection. To examine the possibility that surface water
supplies increase the risk of Giardla infection, a stool survey of one to
three year old children was conducted in two Washington state counties.
This was done to compare the prevalence of Giardia infections among people
served by public water supplies using surface water to oersons served by
deep wells or springs, as well as to estimate Giardia prevalence for young
children.
METHODS
Two Washington State counties (Thurston and Skagit) were selected
for the survey. Thurston County includes the state capitol, Olympia, and
adjoining cities of Lacey and Tumwater. The county includes both an
urban copulation composed primarily of state employees as well as a rural
and small-town population engaged primarily in the forest products indus-
try. Olympia, Lacey and Tumwater residents are served by artesian springs
or deep wells for their water supply. The remainder of the county *s
served by small municipal and individual wells. There are no surface water
supplies in the county.
Skagit County contaitis a number of small to medium-sized towns and a
substantial rural population. The economy is diversified, being based on
farming, fishing, logging and manufacturing. Most drinking water is
obtained from surface sources. Several smaller communities and most
private systems are supplied by wells.
Children were selected from birth certificate records. A total of
1,349 certificates were randomly selected from the two counties. To be
eligible, the child had to be between the ages of one and three at the
ti.ne of the selection. Of the selected certificates, exclusions were
made if the child was deceased (17 children), if the child had a serious
reported birth defect or a birth weight less than 1,500 grams (25 chil-
dren), if the mother was less than age 20 and no father was listed (57
children) and if the mother was an immigrant (15 children). Another 545
children were excluded because the family could not be traced from the
information provided on the !>irth certificate, through directory assist-
ance, or from the county telephone book.
57
-------
The parents of the remaining 690 children were sent letters explaining
the study and requesting their participation. The letter was followed by
a telephone call, at which time the parent, if agreeing to participate,
was interviewed. Some parents with unpublished telephone numbers were
mailed the interview questionnaire. Of the 69 households receiving let-
ters, 91 refused to take part in the survey. Thirty two agreed to parti-
cipate but did not send in the required stool specimens. Fifty families
were sent letters but could not be reached by telephone.
A total of 518 parents (74.9% of those sent letters) were surveyed
with 295 having children born in Skagit County and 223 in Thurston County.
Skagit County was over-sampled to gain a comparable number of persons on
well water supplies as on surfac*1 water supplies.
Only the child on the selected birth certificate was included in the
survey. However, family members were examined if the index child was
positive for any parasite. Participants were paid $5.00 for each of two
samples taken at least one day apart. Stool samples were submitted by
mail to the State Public Health Laboratory in 5% buffered formalin pre-
servative. When received in the laboratory, samples were examined by
direct smear and by formalin-acetate sedimentation. The results of the
stool examination were sent to the parent, and to the physician when
requested by the parent.
RESULTS
Of the 518 children surveyed, 271 were male and 247 female. Ages
ranged from 16 to 34 months. Giardia prevalence was 7.K (37 cases)
for all children in the survey!With the exception of one Trichuris
trichiura, Giardia was the only potentially pathogenic intestinal para-
site found. Non-pathogenic parasites were more commonly found among
Giardia positive than Giardia negative children (p =.001). Nine Giardia
negative children carried nonpathogenic parasites; eight had Entamoeba
coli, one had Entamoeba hartmanni as well as Endolimax nana. Six Giardjia
positive children had nonpathogenic parasites; three had E. col11. two ba"?
E. nana and one had E. hartmanni. Among the 47 asymptomatic family members
of Giardia positive children who submitted stool specimens, 10 (21.3%) were
positive for Giardia. six had E^ nana, three had ]L_ coli and one had E^
hartmanni.
There were no statistically significant differences in Giardia
prevalence by type of domestic water (surface filtered, surface unfil-
tered, well or spring) or by county of birth (Table 26). Combining the
results from both counties revealed no statistically significant increase
in prevalence for working women, children in day care settings or for
families which engaged in many outdoor activities (boating, camping,
swimming or hiking) (Table 27). Significant increases in prevalence were
observed, however, if the child had a history of drinking untreated
surface water (from streams or lakes) (ps.002) or if the family had two
or more children between the ages of three and ten (p=,01) (Table 28). No
Increase in prevalence was observed for children with a sibling under age
58
-------
three.
Additional risk factors were not found when children with either
untreated water or with more than two siblings between ages three and
ten were eliminated.
To estimate the effect of the exclusions and the children not fol-
lowed, the occupational distribution of survey participant fathers (1978
births) were compared to a random sample of Thurston and Skaqit counties
1980 births. The 1980 comparison was necessary since occupation was not
previously recorded on the birth certificate. The results (Table 29) show
.!Mt the survey included a higher percentaqe of professional and adroin-
istr tive occupations and a lower percentaqe of laborers, clerical,sales
and service workers than the random sample (p=.00). No difference was
observed in Giardia prevalence by occupation (p=.72).
DISCUSSION
Although no differences in Giardia prevalence was found between
surface and well drinking water sources, a higher than exoected Giardia
prevalence was observed. Increases in risk of infection appeared for
children consuming untreated surface water and for children with more than
one three-to-ten year old child in the household. This latter finding,
together with the high prevalence of non-pathogenic parasites in Giardia
positive children and the high prevalence of Giardia among household
members of Giardia oositive children, supports the hypothesis of person to
person transmission in these families. The failure to find an increased
risk among children attending a day-care center was unexpected in light
of family-associated risk factors. Giardia infection was not associated
with a recent history of illness, suggesting that many, if not most,
infections in this age grouo are asymptomatic.
The survey did not constitute a random sample of the population of
ona to three year old children in these counties. The differences in the
paternal occupation distribution of survey participants and the sample of
1980 birth certificates was expected from the design of the survey.
Since no differences in Giardia prevalence were observed by paternal
occupation, the importance of this bias is unclear.
The survey findings suggest that intestinal parasites continue to be
a common occurrence among young children despite advances in sanitation
and personal hygiene. The uniformly high prevalence of Giardia in children
of all paternal occupation grouos suggests that the problem is not res-
tricted to any socio-economic segment of the copulation. Since exposure to
untreated surface water occurred commonly among children surveyed, these
prevalence estimates may be higher than would be observed elsewhere. If,
however, these estimates correctly indicate a generally high prevalence of
Giardia infection among children, then the value of treating an asympto-
matic child to reduce the risk of exposing others is questionable.
59
-------
TABLE 26. POSITIVITY BY TYPE OF WATER SOURCE
Type of Water Suoply
Surface unfiltered
Surface filtered
Well or spring
Total
p=.87
Number Surveyed
188
38
292
518
% Giardia
Positive
7.4*
5.5%
8.1*
7.1%
TABLE 27. POSITIVITY BY TYPE OF RECREATION
Type of Activity
Boatinq
Camping
Wadinq pool
Swimming in pool, lake
Number Surveyed
41
101
221
204
% Giardia
Positive
9.8*
5.955
9.0*
8.3*
p Value
P> .
P > .
P > .
P > .
1
1
1
1
or river
Hikinq
32
9.3<
p >. .1
60
-------
TABLE 28. NUMBER OF CHILDREN AND UNTREATED
WATER CONSUMPTION
Exposure
i Surveyed
Number of 3-10 year
old children in
household
0
1
2+
p=.01
232
207
79
% Giardia
Positive
6.0%
5.3%
15.256
Untreated water
consumption
yes
no
o=.0018
106
410
15.1%
5.1%
TABLE 29. OCCUPATION OF PARTICIPANTS
AND CONTROLS
Occupation Group
Prof., administ.
Crafts, sales (insur.,
real estate, etc.)
Laborers, clerical,
sales, services
Students, unemployed
No father
1980 Birth
Certificate
Sample
64
591
230
24
91
Occupation - sample vs survey
Prevalence by occupation
Total
6%
59%
23%
2%
9%
Number
Surveyed
140
294
36
25
22
D=.00
p=.72
Total % Giardia
Positive
27%
57%
7%
5%
4%
7.6%
5.9%
8.3%
8.0%
13.6%
61
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REFERENCES
1. Kirner, J.C., J.D. Littler and L.A. Anqelo. 1978. A waterborne
outbreak of qiardia^is in Camas, Washinqton. J. Am. Water Works
Assoc. 70:35-40.
2. Ritchie, L.S. 1948. An ether sedimentation technique for routine
stool examinations. Bull. U.S. Army Med. Dept. 8:326.
3. Faust, E.G., J.S. D'Antoni, V. Odotn, M.J. Miller, C. Peres, W.
Sawitz, L.F. Thomen, J. Tobie and J.H. Walker. 1938. A critical
study of clinical laboratory technics for the diaqnosis of protozoan
cysts and helminth eqqs in feces: I. Preliminary communication.
Am. J. Troo. Med. 18:169-183.
4. Sheather, A.L. 1923. The detection of intestinal protozoa and mange
parasites by a flotation technique. 1. Como. Path. & Therap. 36:266-
275.
5. Oavies, R.B. and C.P. Hibler. 1979. Animal reservoirs and cross-
species transmission of Giardia. In Waterborne Transmission of
Giardiasis. (USEPA, Cincinnati) po 104-126, EPA-600/9-79-001.
6. Shaw, P.K., D.O. Prodsky, B.T. L.yman, B.T. Wood, C.P. Hibler, G.R.
Healy, K.I.E. MacLeod, W. Stahl and H.G. Schultz, 1977. A community-
wide outbreak of qiardias^ with evidence of transmission by a munic-
ipal water supply. Ann. Int. Med. 87:426-432.
7. .lakubowski, W. 1978. Waterborne giardiasis. In Waterborne Trans-
mission of Giardiasis (USEPA, Cincinnati) pp 193-210, EPA-600/9-79
-001.
8. Lippy, E.C. 1978. Tracinq a qiardiasis outbreak at Berlin, New
Hampshire. J. Am. Water Works Assoc. 70:512-520.
9. Frost, F, 8. Plan, B. Liechty. 1980. Giardia prevalence in com-
mercially traoped mammals. J. Env. Health 42:245-249.
10. Wriqht, R.A., H.C. Soencer, R.E. Brodsky, and T.M. Vernon. 1977.
Giardiasis in Colorado: An epidemioloqic study. Am. J. Epid.
105:330-336.
11. Breslow, N.E., N.E. Day, K.T. Halverson, R.L. Prentice, C. Saba.
1978. Estimation of multiple elative risk functions in matched
case-control studies. Am. J. tpid. 108(4):299-307.
62
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REFERENCES (continued)
1?. Halverson, K.T. 1978. M.S. Thesis, University cf Washinqton.
13. Black R.E., A.C. Dykes, S.P. Sinclair, J.G. Wells. 1977. Riardiasis
in day-care centers: Evidence of person-to-person transmission.
Pediatrics 60:486-491.
63
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Appendix A
Case and Control Questionaire
64
-------
Date
Tine
Results
Reference Nirrt ar.
Lab. slip date _
Phone book entry,
Physician name .
Physician phone,
Interview date
Interviewer na»ne
Patient Name
Patient Address
Phone (Home)
Occupation
Spouse Occupation
Place of Birth
Length of residence
at present address
City of
County of
Length of residence
(Work)
1n Hash.
Former residences: City/State
(3 years) City/State"
City/State'
Illness History
Date of diagnosis
Duration of Illness
Interviewee
Relationship to patient
Patient's Sex Age.
Ht. Wt.
Number 1n household
sex
age
Length
|Length
' Length
Date Illness began:
Date of first visit to phys1c1ar_
Indicate which, 1f any, of the following symptoms you experienced:
Nausea Vomiting Pain 1n upper abdomen Loose stools
Constipation Increase In number of bowel movements Gas
Loss of appetite Wt. Loss Bloating Weakness Fatigue
Fever/Chills Other symptoms
If no symptoms, reasons for submitting stool sample _^
Cramps _
65
-------
Which drug were you given: Flagyl Hetrcnldazole Atabrlne Don't Know.
Other (specify) No drug (reason?) ^__^_______^_______
Now long between beginning of treatment and end of symptoms?
Were you being treated for any other Illness ft that tine?
If so. what type?
When did you last have a routine check-up?
Have you seen a doctor for a stomach or Intestinal problem other than Glardla?
If so. what
When did you last see a doctor for any Illness or health problem other than
Glardia?
Were other family members or friends affected? Yes No
If so, when , Relationship Name Ref. §
when Relationship Name Ref. I
when Relationship Name Ref. I
Pets Do you have Indoor pets? yes/no
If so. what type (1) Age (1)
(2) (2)
Where do they sleep?
Do you have outdoor peU or other animals?
Stool sample kits for pets sent: Number Date
Results: II - animal Indoor?
12 - animal Indoor?
*3 - animal Indoor?
Travel During the 2 months prior to onset of symptoms, did you do any
a. Foreign travel (outside U.S.) yes/no When
If so, where?
Did symptoms begin there?
If not, how long after return did they begin?
What was the source (usual) for drinking water?
66
-------
b. U.S. (outside Wash.) yes/no When?
Where?
Old symptoms begin there?
If not, how long after return did they begin?
Did you engage In any outdoor activities while there? Circle: No Day
Camping Backpacking (overnight hikes) Fishing Hunting Boating
Swimming Water Skiing Picnicking Snow skiing Other __
What was the source of your drinking water?
Did you drink water from lakes, streams, etc.?
Within Wash. yes/no When?
Where?
Did symptoms begin there?
If not, how long after return did they begin?.
Did you engage In any outdoor activities while there? Circle: No Dayhikes
Camping Backpacking (overnight hikes) Fishing Hunting Boating
'Swimming Water Skiing Picnicking Snow skiing Other
What was the source of your drinking water?
Did you drink water from lakes, streams, etc.?
If yes, did you treat the water before drinking It?
Domestic Water Supply
a. What Is the source of home water?
City Well Other
b. Do you purchase Irrigation water?
c. What type of sewage system is used in your home?
Sanitary sewer system Septic tank Other.
d. How many bathrooms do you have In your home? _______
67
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Public Exposures - Other
a. Are you a vegetarian?
b. Did you go swimming In the 2 months prior to the onset of the symptoms?
yes/no Pool
Streams, lakes, rivers
If a child, has he/she attended a nursery school or day care center within
th;- 2 months prior to the onset of symptoms? yes/no
Where?
d. If under the age of 10. number of different playmates per week (excluding
nursery school or da> care center playmates)
e. If an adult, have you had contact with children under the age of 3 yes/no
Under the age of 10? ___^_ yes/no
If yes, what was that contact? (e.g. babysitting, youth group activities,
neighbor children, relative?) ________^_____________
f. Other possible exposures:
68
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CONTROL
CASE
Name of
Phone •Book Entry
Name of
Hatched control
Address
Phone
Case Reference t_
Age of Case
Sex of Case
Date of report
of Illness
Date of follow-up
Date of Control Interview
Age Sex Ht.
Place of Birth
Occupation
Spouse Occupation
Length at Present Address
Former Residence: City
(3 years) City
City
Ut.
State
State
State
Total Length of Residence in Washington
Number in Household
Sex
Age
Length
Length
length
Illness History
When did you last have a routine check-up?
When did you last see a doctor for any Illness or health problenu
Nave you ever seen a doctor for a stomach. Intestinal or bowel problem?
If $o. what was It? (e.g. colltus, ulcer)
Have you ever suffered with chronic diarrhea (more than one weeks duration)?
yes/no
69
-------
-2-
Travel - Foreign
Have you traveled outside of the United States in the last 2 months? yes/no
If so, where? When?
Did you suffer front stomach problems or diarrhea while you were there?
Dtd you suffer from any diarrhea within 3 weeks of returning home?
Travel - United States
Have you traveled outside of Washington State in the last 2 months? yes/no
If so, where? When? •
Did you engage in any outdoor activities while there? Please circle: Day hikes
Camping Hunting Boating Swimming Water skiing Backpacking (overnight hikes)
Picnicking Snow skiing Fishing Other (specify)
Did you drink water from lakes, streams, rivers, etc.?
Did you treat the water before drinking it? yes/no Haw?
'.ravel - Washington
Have you traveled within Washington State in the last 2 months?* yes/no
If so, where? When?
Did you engage In any outdoor activities in the last 2 months In Washington State?
Please circle: Day hikes Camping Hunting Boating Swimming Water skiing
Backpacking (overnight hikes) Picnicking Snow skiing Fishing
Other (specify)
If so, where? • When?
Did you drink water from lakes, streams, rivers, etc.? _'_
Did you treat the water before drinking it? yes/no How?
70
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-3-
Kater Supply
How many glasses of the following liquids do you drink per day:
Water Juices/drinks made with water (c-9-, lemonade, Iced tea,
Kool Aid)
Milk Coffee/tea Canned or bottled beverages
What 1s the source of home water?
City Well Other (specify)
What type of sewage system 1s used In your hone?
City Sewer System Septic Tank Other (specify)
How many bathrooms do you have In our home?
When hlkfng or traveling in remote mountain !rc-
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Appendix B
Coding Instructions
72
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WDING USED FOR VARIABLES
VARIABLE DESCRIPTION
CODING
Sex
Age
County/City
Family Size
Washington Residence/Present Residence
Symptoms
vomiting
nausea
pain 1n abdomen
loose stools
cramps
constipation
change 1n bowel movements
gas
loss of appetite
weight loss
floating
weakness
fatigue
fever/chills
other symptoms
No Symptoms/Reason for Submitting Stool
Sample
Drug Prescribed
Indoor Pets
H male
F female
0 <1 year
Actual number 1 year or more
Federal codes
Actual number
0 <1 year
Actual number 1 year or more
1 yes
2 no
1 foreign travel
2 exposed .0 positive person
3 recent 1 nlgrant
4 exam for -.ther health problem
5 exposed t•• Glardla source
1 Flagyl
4 don't know
5 Atabrlne
6 other drug
7 no drug
8 combination/multiple pres-
cription of drugs
0 none
1 young dog
2 adult dog
3 multiple dog
4 young cat
5 adult cat
6 multiple cat
7 combination cat and dog
8 other animal
73
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CODING USED FOR VARIABLES (CONTINUED)
VARIABLE DESCRIPTION
CODING
Foreign Travel/
Out of State Travel/
Washington Travel
Occurrence of Illness Since Travel
Glasses of Water Consumed
Method of Waste Disposal
Restaurant Visits Per Month
Fast Food Restaurant Visits Per Month
Swimming
Consumption of Untreated Water
Immigrant/Migrant
Occupation/Spouse Occupation
1 yes
2 no
0 while away
1 one week or less
Actual number >1 week
97 dally/frequent exposure
98 no symptoms
Actual number
1 sewer
2 septic tank
3 other
Actual number
AcUal number
0 none
1 private pool
2 public pool
3 river
4 lake
5 combination pool and natural
6 combination of pools
7 combination of natural
8 salt water
1 yes
2 no
1 yes
2 no
01 professional, technical
02 managers, administrators
03 sales workers
04 clerical
05 craftsmen
06 operatives
07 transport equipment operatives
08 laborers except farm
09 farmers and fan.i managers
10 farm laborers
11 service workers
12 private household workers
13 hotneraaker
14 retired
1$ Institutionalized
16 student
17 unemployed
18 other
74
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CODING USED FOR VARIABLES' (CONTINUED)
VARIABLE DESCRIPTION
CODING
Place of Birth
Household Infants 0-2 Years
Household Children 3-10 Years
Date Illness Began
Duration of Illness
Months Since Last Check-up
Previous Enteric Problems
Months Since Last Physician Visit
For Illness
Contact With Positive Person
Pet Sleeping Place
Own Outdoor Farm Animals
Travel Place-County
See Travel Place below
0 none
Actual number 1-7 Infants
8 eight or more Infants
0 none
Actual number 1-7 children
8 eight or more children
Actual month and year
1 one week or less
Actual number >1 week
98 ninty-elght weeks or more
1 one month or less
Actual number >1 month
98 ninety-eight or more
1 yes
2 no
1 one month or less
Actual number >1 month
98 ninty-elght months or more
1 confirmed case of glardlasls
2 suspected case/symptomatic
3 none
1 Indoors
2 outdoors
3 Indoors, confined space
1 yes
2 no
001 Adams
003 Asotln
005 Benton
007 Chelan
009 Clallam
Oil Clark
013 Columbia
015 Cowl Hz
017 Douglas
019 Ferry
021 Franklin
023 Garfleld
025 Grant
027 Grays Harbor
75
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CODING USED FOR VARIABLES (CONTINUED)
VARIABLE DESCRIPTION
COOING
Travel Piece-County (Continued)
Travel Place-State
029 Island
031 Jefferson
033 King
035 KUsap
037 KHtltas
039 Kllckitat
041 Lewis
043 Lincoln
045 Mason
047 Okanogan
049 Pacific
051 Pend Orellle
053 Pierce
055 San Juan
057 Skagit
059 Skamanfa
061 Snohomlsh
063 Spokane
065 Stevens
067 Thurston
069 Wahkiakum
071 Walla Walla
073 Whatcom
075 Whitman
077 Yaklma
078 Multiple
079 Unknown
222 Mo county travel
801 Alabama
802 Alaska
803 Arizona
804 Arkansas
805 California
8u6 Colorado
807 Connecticut
808 Delaware
809 District of Columbia
810 Florida
811 Georgia
812 Hawaii
813 Idaho
814 Illinois
815 Indiana
816 Iowa
817 Kansts
818 Kentucky
819 Louisiana
820 Maine
821 Maryland
822 Massachusetts
823 Michigan
824 Minnesota
825 Mississippi
76
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CODING USED FOR VARIABLES (CONTINUED)
VARIABLE DESCRIPTION
CODING
Travel Place-State (Continued)
Travel Place-Foreign Country
Outdoor Activities
day hikes
camping
backpacking
fishing
boating
water skiing
picnicking
snow skiing
other
' 826 Missouri
827 Montana
828 Nebraska
829 Nevada
830 New Hampshire
831 New Jersey
832 New Mexico
833 New York
834 North Carolina
835 North Dakota
836 Ohio
837 Oklahoma
838 Oregon
839 Pennsylvania
840 Rhode Island
841 South Carolina
842 South Dakota
843 Tennessee
844 Texas
845 Utah
846 Vermont
847 Virginia
848 Washington
849 West Virginia
850 Wisconsin
851 Wyoming
888 Multiple State
222 No state travel
081 U.S. Possessions
082 Canada
083 Mexico
084 South and Central America
085 Europe-Western
086 Europe-Eastern
087 Middle East and Northerr, Africa
088 Southeast Asia
089 Russia
090 Africa
091 Australia and South Pacific
092 Northern Asia
093 Multiple foreign country
222 No foreign travel
1 yes
2 no
77
-------
CODING USED FOR VARIABLES (CONTINUED)
VARIABLE DESCRIPTION
COOING
Doneitlc Water Source/Class
Domestic Water Source
surface unflltered
surface filtered
well
spring
Number of Bathroons 1n Home
Nursery School/Day Care Hone Attendance
Playmates
All Unknown Information
MOO residences
2 community >10 residences
3 recreation/commercial
4 cotwriur.lty <10 residences
5 private, single residence
1 primary water source
2 secondary water source
7 not used as water source
Actual number
1 yes
2 no
Actual number
9
78
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Appendix C
Occupation Stains Codes
79
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